It's an in-universe "rule", made in reaction to a meta aspect of the storytelling.

I mean, basically it's saying "Hey, us bad guys have a tendency to turn on each other due to being...well...badguys. I don't like this, so we're going to stop it, by purging everyone down to just two people, because that means it's less likely we will turn on each other." *spoiler: it doesn't, it just narrows down the number of targets*.

But, the entire thing of "evil turns on itself" isn't unique to Sith, it's one of the most staple aspect of storytelling in human storytelling. It's one of the ways that a downtrodden, hopelessly outnumbered Band of Heroes, are able to destroy the Big Bad. The fact that the bad guys frequently lose sight of the bigger picture, due to personal ambition and greed, and turn on each other at inopportune times, is how the plucky band of adventurers are able to live long enough to actually win, which they are supposed to do, because they are the Protagonists of the story.

And it feels to me like the author who came up with that silly rule, just simply doesn't like that particular trope in storytelling, so he decided to permanently rewrite the entire Star Wars canon structure, due to his personal distaste of "The Bad Guys Lose, because they are Bad Guys and turn on each other" trope.

And the funny thing is, this isn't even the only time this has been done, the whole "Hey, maybe we shouldn't fight each other so much" thing. Dragonlance did it too, but in that series, they were at least realistic enough to acknowledge that 2 people trying to uphold an entire mythic ethos, and establish powerful dominance in a galaxy spanning society for long term, is pretty much impossible. In the...4th Age of Dragonlance I think? Maybe 5th Age? I forget. Anyway, the followers of Takhisis, the Goddess of Evil, basically stopped fighting each other, and created an entire Order of Dark Knights, who worked together, and pretty much conquered the world. Why? Because they actually had the resources to pull it off. 2 of them wouldn't have accomplished jack and shite. And they still lost in the end. Why? Because they were the antagonists, and that's their job. To be the conflict the protagonists overcome and triumph against.

So yeah, the Rule of 2 is silly (though I do acknowledge the name has a nice dramatic ring to it) in my opinion, and I think that's why. Just felt like sharing that when it popped in my head.

One aspect of the Rule of Two that you're overlooking is that (Palpatine aside) was that it was very much the intent that the apprentice would at one point overthrow/depose the master; "One to embody power, the other to crave it" That way, the Sith legacy would remain strong and each subsequent apprentice would be highly capable, both in terms of Force power and cleverness. It also ensured the master wouldn't rest on their laurels and would themselves remain strong and capable for as long as possible; if you know darn well that your apprentice is looking for a prime opportunity to kill you, that's going to keep one on their toes.

Palpatine was the only Sith of that lineage to be arrogant enough to presume that he wouldn't really need a successor, and that he was the ultimate expression of the Sith philosophy, especially in the wake of Vader being so badly damaged (physically and psychologically).

The Rule of Two is social Darwinism at it's simplest, with the long term goal that eventually the Sith would have their revenge on the Jedi. And given how the galaxy shook out in the wake of Palpatine's big gambit during the prequels, I'd say it worked out pretty well for them.

Then again, much like the Jedi philosophy of "avoid attachments and don't let your emotions overrule your rational thinking," it's a mindset that's simply too foreign to most human beings to seem even remotely feasible much less sensible. Both are in defiance of the general human trend to form bonds and communities with our fellow human beings, the Sith to stand alone and the Jedi to retain a sense of detachment from the masses.

25 minutes ago, Donovan Morningfire said:

One aspect of the Rule of Two that you're overlooking is that (Palpatine aside) was that it was very much the intent that the apprentice would at one point overthrow/depose the master; "One to embody power, the other to crave it"

I am aware of that, but it doesn't actually "solve" the problem that the Rule of Two was meant to solve. Designing it so that you are still fighting each other for power doesn't remove the initial flaw being addressed, namely that of the Sith fighting each other for power. The fundamental issue is still there, it's just now been limited to 2 people, instead of potentially thousands.

25 minutes ago, Donovan Morningfire said:

That way, the Sith legacy would remain strong and each subsequent apprentice would be highly capable, both in terms of Force power and cleverness. It also ensured the master wouldn't rest on their laurels and would themselves remain strong and capable for as long as possible; if you know darn well that your apprentice is looking for a prime opportunity to kill you, that's going to keep one on their toes.

Except it didn't keep the legacy strong. It brought it to the brink of extinction (and after Return, actual extinction). And if not for a few really stupid decisions by the Jedi early on in the PT, the entire plan would've been thwarted, and the Sith legacy ended. Palps would've been killed (because no way was he going down easy), and Anakin wouldn't have been pushed to the Dark Side. That's not ensuring the legacy's longevity, that's risking the entire thing on one person. There is an old saying about all your eggs in one basket. And this is a basket that's apparently encouraged to snap at your hand while your trying to put eggs in it, risking you dropping the thing and ruining all your eggs.

As to it keeping you on your toes, apparently not very well, as Palps completely didn't consider that Darth Vader might have a problem with him killing his son. A point of conflict for Vader, one that Palps even commented on in RotJ. "I wonder if your feelings on this matter are clear...Lord Vader." Implying he wasn't certain that Vader wasn't emotionally invested in his son. A point that, you know, when later slowly, killing said son, while he's begging his father for help...after an extended fight where he kept trying to convince Vader to give up his ways, further reinforcing the idea of "Hmm, maybe I shouldn't assume Vader will side with me against his son." That's a huge slip up for someone who is supposed to be "on his toes" when his apprentice is around.

25 minutes ago, Donovan Morningfire said:

Palpatine was the only Sith of that lineage to be arrogant enough to presume that he wouldn't really need a successor, and that he was the ultimate expression of the Sith philosophy, especially in the wake of Vader being so badly damaged (physically and psychologically).

Except he did think he needed a successor. That's the whole crux of the final conflict in RotJ. "Gooood! Gooood! Your hate has made you powerful! Now fulfill your destiny, and take your fathers place at my side" He was clearly trying to upgrade his apprentice to a newer model, per the Rule of Two as you are suggesting.

25 minutes ago, Donovan Morningfire said:

The Rule of Two is social Darwinism at it's simplest,

I agree, and social Darwinism is a load of shite, which is why I find the Rule of Two to be a load of shite

25 minutes ago, Donovan Morningfire said:

The Rule of Two is social Darwinism at it's simplest, with the long term goal that eventually the Sith would have their revenge on the Jedi. And given how the galaxy shook out in the wake of Palpatine's big gambit during the prequels, I'd say it worked out pretty well for them.

Except it didn't, that's my whole point. Palp's Empire lasted roughly 1 generation, long enough for the son of his apprentice to grow up and destroy him. And, at the end of that film, the Sith are gone. Extinct. Why? Because there were only 2 of them, and they were still fighting each other, and both died in a very large scale war that was raging around them. That's not insuring the long term stability of the Sith Philosophy, that's banking that every single person along that Sith tradition, isn't a cackling nutjob (something they are kind of prone to, given how most Dark Side users behave irrationally and violently), and that they won't be so ambitious to grasp for things beyond their control, in a way that might risk their life, and the life of their apprentice (someone likely to be near them, and thus at Ground Zero of whatever retribution they have fostered). Sure they almost killed the Jedi, reducing them down to two, but since the Jedi have on such rule about "only 2 of us", in the aftermath, it was assumed that Luke would train a large number of people to be Jedi, something that the EU frequently adopted as "canon", and the Last Jedi also confirmed was done. Meaning they won. Which is to be expected of course, they are the protagonists, but the Sith were dead. Gone. In one action, the only 2 Sith were killed, insuring their legacy would be lost forever.

25 minutes ago, Donovan Morningfire said:

Then again, much like the Jedi philosophy of "avoid attachments and don't let your emotions overrule your rational thinking," it's a mindset that's simply too foreign to most human beings to seem even remotely feasible much less sensible. Both are in defiance of the general human trend to form bonds and communities with our fellow human beings, the Sith to stand alone and the Jedi to retain a sense of detachment from the masses.

I agree, the Jedi "no emotions" thing, or at least the interpretation by fans that it means "you must carve out your emotions, and act like a Vulcan to be a Jedi" is equally flawed. I personally don't think that's what the "There is no emotion, there is only peace" means, and that it simply means "Don't let your emotions rule your actions, take a moment, calm yourself, be at peace, and then choose your actions." Is what it means. But that's another discussion for another day. The avoid attachments bit is just not possible for humans, except for anti-social shut ins. But the "don't let your emotions overrule your rational thinking" isn't actually as far fetched for humanity as you might think. A lot of philosophies preach that kind of mindset when dealing with life.

I think the Rule of Two is a rationalization, more than a justification, for killing off most of the Sith. It was a way for the most powerful Sith to limit the competition he might otherwise face. The ultimate victory of the Sith was likely a secondary concern to the ultimate victory of the Master. An apprentice was a a powerful tool first, and a way to keep the tradition going second. But I don't think that most Sith Masters worried too much about what would happen to the Sith if they personally were killed.

Keep in mind I don't know much EU/Legends, but I believe the main problem the Rule of Two was meant to solve was the loss of power/knowledge.

For instance, if one Master had five apprentices, those apprentices could gang up on the Master and kill him, even though they weren't fully trained and had only half of the knowledge and experience of the Master, and then a lot of useful knowledge and skills would be lost.

On the other hand, even if every Master was limited to one apprentice, but there could be multiple Masters, the apprentices could get together to Strangers on a Train each others' Masters, resulting in the same loss of knowledge.

But if there's only one Master and one Apprentice, those problems go away. The Apprentice can't gang up on his Master and overwhelm superior power with numbers, he has to be legitimately better at being a Sith (or at least substantially equal) to have a shot.

It wasn't meant to stop the "Evil turns on itself" problem, because that's what being a Sith is. It was meant to ensure that when it happened, no progress was lost in the exchange.

the other problem with the rule of 2 is it assumes there is only one source of there being sith. even though we have examples of sith coming from non living sources..

1 hour ago, Absol197 said:

For instance, if one Master had five apprentices, those apprentices could gang up on the Master and kill him, even though they weren't fully trained and had only half of the knowledge and experience of the Master, and then a lot of useful knowledge and skills would be lost.

On the other hand, even if every Master was limited to one apprentice, but there could be multiple Masters, the apprentices could get together to Strangers on a Train each others' Masters, resulting in the same loss of knowledge.

But if there's only one Master and one Apprentice, those problems go away. The Apprentice can't gang up on his Master and overwhelm superior power with numbers, he has to be legitimately better at being a Sith (or at least substantially equal) to have a shot.

But you have the exact same risk of loss of knowledge with only 2 people who know the knowledge in the first place. I mean, the Jedi teachings were represented as being "all but extinct", since they were reduced to just Yoda and Ben. Yet the same number of Sith is somehow "strong and vital, and promotes the continuation of the knowledge?" I just don't buy that. Anything that gets reduced down to that small of a number, is on the verge of being wiped from existence. Excluding things like recorded data and teachings of course. But if we're operating under the "you have to learn it from another person" logic, which is what this Rule of Two works off, and ignores things like holocrons that anyone could find, it's just too fragile of a premise, to try and continue a tradition.

1 hour ago, Absol197 said:

It wasn't meant to stop the "Evil turns on itself" problem, because that's what being a Sith is. It was meant to ensure that when it happened, no progress was lost in the exchange.

Except the "evil turns on itself" reason, is the very reason I've heard for years as to why the Rule of Two exists. I mean the Wookieepedia entry on the Rule of Two itself even states, that Darth Bane created the rule, because he realized that "Sith greed and in-fighting led to their destruction". That's a direct quote from the entry.

And when your entire philosophy has to hinge on the idea that "we don't end up with one crazy egomaniac, to screw it all up for everyone", you aren't really thinking long term Because that's apparently all it took to destroy the Sith. One guy, Palpatine specifically, to be so pants-on-head crazy for power and his own prestige, to screw up and get both himself, and his apprentice killed in one day, thus ending the cycle of "The Apprentice assumes the Master when he defeats him" thing.

It really does just feel like an author trying to counter-trope the "evil turns on itself" trope, ironically by canonizing an equally used trope of "the student of evil kills the master of evil and takes his place"

You're probably right . I just hadn't seen the point brought up yet, so I did so myself. I make no statements about how logical I find the argument .

The Rule of Two makes perfect sense if you've ever played Star Wars: The Old Republic.

In the Republic class story missions, most of the time your working against the Sith Empire, or allies of the Sith Empire, or people on the Sith Empire's payroll in one form or another.

In the Imperial class story missions, at least half the time (and sometimes for the entire class story for some classes), you're working against other elements of the Empire. Trying to take down your master because he's a huge (literally and figuratively) jerk, usurping your master's powerbase for yourself, setting your powerbase against another Sith Lord's in some ancient tradition of dueling with resources instead of lightsabers, turning on anyone and everyone because that's the right move for you at the given time and screw the consequences for anyone else. . . honestly, it's a miracle the Sith Empire still exists after the repeated applications of gun to foot. The Rule of Two short-circuits a lot of that.

Also, as has been pointed out, apprentices ganging up on masters (and then turning on each other more likely than not) and masters attacking each other means that each successive generation of Sith is weaker than the last, getting less training and overcome fewer challenges to reach the pinnacle of the Sith Order, since everyone above them has been killed off already. Under the Rule of Two, the apprentice should fight the master when both are at the absolute height of their power, so that each successive generation of Sith grows stronger (how well this works in practice is debatable. . . Palpatine all but states he murdered his master in his sleep, so didn't exactly overcome him via raw skill or Force ability, but then again EU sources state Palpatine himself learned to never sleep so he wouldn't go the same way as his master, so maybe there's still something to that. . .)

You also kind of need to understand Darth Bane's frame of mind, and background, when he created the Rule of Two. First, he was recruited into a Sith Order called the Brotherhood of Darkness, which sought to avoid the infighting by declaring that all Sith were equal, hence the name. They would work together to achieve common goals and focus their energies in the same direction. Bane eventually decided that the Brotherhood of Darkness was really no different than the Jedi, who had a similar philosophy for how to get things done, and the Brotherhood's leader even mused, in his weaker moments, that maybe the Brotherhood and Jedi were not so different, and was concerned that both were falling into an abyss of grey, neither one able to claim the heights of power exemplified by Light and Dark. And the Brotherhood was really only held together by the leader's Force-enhanced charisma, his ability to basically mildly mind-frell everyone around him into agreeing with what he said. If he died, or lost his ability to control them, they whole order would have collapsed. There were already signs that the stress was getting to him and he was going mad, and one character seriously considered abandoning him and his insane cause before he laid an extra-strength whammy down on her.

Bane considered it of paramount importance to the core of what it means to be Sith that the struggle for power, for achievement, for greatness, was ever-present, that a Sith should never be able to let their guard down, because weakness was death. Yet you can't have just one Sith, since that Sith can't live forever, can't embody the Sith philosophy past the end of his or her life. Thus, you need an apprentice, but having too many means they'll gang up on you and kill you before they've reached the pinnacle of their strength, and thus again are the Sith as a whole diminished. Darth Revan, via holocron, actually laid out the foundation for the Rule of Two, stating that a Sith should have no more than one apprentice for this exact reason. Bane just went a step further, stating that there should be only one Sith Lord (I believe Revan's holocron actually stated something similar, but wasn't sure how to really make the idea work in practice).

Given what Darth Sidious was able to accomplish, it remains a fact that the Rule of Two got something right, as he was perfectly poised and trained and prepared to utterly destroy the Jedi and the Republic, something no Sith Order before him had quite accomplished (some had come close to destroying the Jedi, but the Republic had remained fairly strong). Is only allowing two Sith in existence at any one time a huge gamble? Absolutely, but that allowed them to remain hidden for a thousand years, and when the time was right, spring upon an unwary Jedi Order and Republic with such subtlety and skill that neither saw them coming until it was too late. Having an army of Sith in hiding, backstabbing each other constantly, would be just as much, if not more, of a gamble, because they all might kill themselves before they get a chance to bring down the Jedi, or might be discovered and wiped out by the Jedi, having been weakened by eternal infighting. Any way you care to slice it is a problem, so the question then becomes which one minimizes risk while maximizing reward? A small order, adept at moving in the shadows and behind the scenes, playing a long-term game of Go while the Jedi are working on Go Fish.

The rule of two has never felt like a hard and fast rule to me. More like guidelines ala Pirates of the Caribbean. We've seen a lot of masters playing with the idea of multiple apprentices and no one is yelling heresy. That being said after reading the now non-canon Bane novels, I feel he was more breaking away from the whole academy hogwarts of the sith scenario it was growing into and more delving into the idea of pouring all of the training one had into one apprentice as best as possible and the apprentice having the role of being worthy of that information and the master staying alive long enough to pass that information on to a worthy successor.

I do to however find it not the best as it only takes one bad day to ruin the Sith forever. So yes the rule of two was probably not the brightest philosophy.

Side thought though, do you really think we've seen the last of the Sith in the future timeline of Star Wars, even with the rule of two?

39 minutes ago, Drig said:

The rule of two has never felt like a hard and fast rule to me. More like guidelines ala Pirates of the Caribbean. We've seen a lot of masters playing with the idea of multiple apprentices and no one is yelling heresy. That being said after reading the now non-canon Bane novels, I feel he was more breaking away from the whole academy hogwarts of the sith scenario it was growing into and more delving into the idea of pouring all of the training one had into one apprentice as best as possible and the apprentice having the role of being worthy of that information and the master staying alive long enough to pass that information on to a worthy successor.

I do to however find it not the best as it only takes one bad day to ruin the Sith forever. So yes the rule of two was probably not the brightest philosophy.

Side thought though, do you really think we've seen the last of the Sith in the future timeline of Star Wars, even with the rule of two?

**** if you are paying attention Palpatine did so. Pretty sure he was working with Dooku before Darth Maul wasnt half the man he used to be.

3 hours ago, ErikModi said:

The Rule of Two makes perfect sense if you've ever played Star Wars: The Old Republic.

I have played SWTOR, for many years thank you very much, and I disagree with you. So stating that "it makes sense if you know about X" isn't actually fact, it's just an opinion.

2 minutes ago, KungFuFerret said:

I have played SWTOR, for many years thank you very much, and I disagree with you. So stating that "it makes sense if you know about X" isn't actually fact, it's just an opinion.

So? Isn't everything here an opinion?

Just now, ErikModi said:

So? Isn't everything here an opinion?

Yes but saying things like "It makes sense if you've done something", when there are plenty of people who actually have done that, and don't share the posters opinion, tend to imply a "well you just don't get it" kind of tone. Saying things like "Batman vs Superman makes sense if you've read the comics." which is just false, since many people who religiously read those comics, think the movie sucks.

5 minutes ago, KungFuFerret said:

Yes but saying things like "It makes sense if you've done something", when there are plenty of people who actually have done that, and don't share the posters opinion, tend to imply a "well you just don't get it" kind of tone. Saying things like "Batman vs Superman makes sense if you've read the comics." which is just false, since many people who religiously read those comics, think the movie sucks.

Batman v Superman sucked because it was rushed and tried to do too many plot lines at once and I love DC comics.

23 minutes ago, KungFuFerret said:

Yes but saying things like "It makes sense if you've done something", when there are plenty of people who actually have done that, and don't share the posters opinion, tend to imply a "well you just don't get it" kind of tone. Saying things like "Batman vs Superman makes sense if you've read the comics." which is just false, since many people who religiously read those comics, think the movie sucks.

Okay, I'm sorry. I didn't realize I needed to preface everything with in my opinion.

In my opinion, seeing the utter stupidity of the Sith Empire in Star Wars: The Old Republic in shooting themselves in the foot repeatedly in every single class questline demonstrates the Rule of Two is superior to what came before. Especially when you get to Makeb and it's outright stated that, if the Sith don't get this shiny new Unobtanium, they're doomed to be curb-stomped by the Republic. Because they've lost whole fleets and armies, to say nothing of promising and powerful Sith, to pointless arm-wrestling contests between Sith Lords because one of them wants another's position, title, rank, armies, resources, castle, or office.

In my opinion, I think that you choosing to discard everything I said because you believe I stated an opinion as fact is missing the point of what I was trying to say. Not necessarily that the Rule of Two was perfect, but that it makes sense given the failures of the previous Sith Orders and where and who Darth Bane was when he decided on it. And, not in my opinion but in point of fact, the Rule of Two Sith managed to stay stable and in existence for a thousand years, topple the Republic, create a galaxy-spanning Sith Empire, and effectively wipe out the Jedi (that they did return notwithstanding). So there must be some merit to it.

In my opinion, I think you should reread what I wrote before, from the perspective that it is my opinion sprinkled with facts to support it, and see if it has any merit on that basis, rather than dismissing it and me completely on the basis of the logical fallacy that "opinion, not fact, therefore not relevant."

I read your opinion, weighed it, balanced it, decided I disagreed with it, and attempted to show you why I disagreed with it, not necessarily to change your mind, but to demonstrate why others might think the Rule of Two is not "really silly," and why, from a certain point of view, it does make sense. If you still don't like it, great, fine, good for you. But please give my opinion the same amount of respect I give yours.

10 minutes ago, ErikModi said:

I did give your opinion the same respect, I disagreed with it, and still do, despite having played the same game as you. And things like "the jedi not being wiped out not withstanding" and things like "the Sith were completely wiped out" means the plan didn't work. The Sith empire survived for thousands of years prior to the Rule of Two, so saying that "it worked for a long time" when other methods worked too, doesn't help the stance that it's a good philosophy. The final result, is that they didn't accomplish their goal (Destroy the Jedi), and they didn't survive (they were wiped out, since only 2 of them existed). Rule of 2 didn't work.

Writing a series of thesis paper-length posts about ANYTHING in the Star Wars universe is silly, and I just realized why. Wait. No. No, I've known why for a long time...

Hate to break it to you (anyone who didn't know), but Star Wars is the KING of worldbuilding fails. The number of bits of irrevocably canon lore and world-elements that had absolutely no forethought to what they meant, or history to where it came from, or would go, is innumerable in this IP.

There was no grand cohesive vision for any of this universe, even by the time this nugget popped out of Yoda's mouth in 1999, and a grand vision that was there from the start is what would be required to make this initial statement, or the mind numbing debate that spring from its loins, mean anything at all.

It had just barely gotten its act together by the time Drew Karpyshan was tasked with fleshing the premise out in the Bane Trilogy, 6 years later. But by that time he of course had this mish mash of decades of meaningless, disparate canon elements that he had to make into a novel.

You're critiquing a marketing maneuver.

Wow, if playing a dice and role play game about a fictional universe wasn’t nerdy enough

Rule of two is dumb (opinion), if an entire army can hide in the Unknown regions then why couldn’t a repository of Sith knowledge as well as a school (fact). Thankfully dark siders don’t have to be Sith, just as paragons of the light don’t need to be Jedi.

*kicks soapbox in*

Rule of 2 was designed to breed stronger Sith every generation and it worked well. Between Revan (who first noted the Sith were doomed to fail due to backstabbary) and Bane who executed on it (HEEHEE I made a killing joke), the design was to prevent a group of weak Sith from taking down a stronger opponent and in turn weaken the whole.

If I recall correctly Revan laid out his reasoning in KOTOR when the PC is at the Sith academy. Bane...well he was Bane and read Revan's holocron.

GL shorthand for Anakin's motivation to becomemVader. One to have power and the other to crave it, which Anakin exhibits in ATOC during his chats with Padme

I'll just gently place this here...

http://starwars.wikia.com/wiki/Rule_of_One_(Palpatine's_Doctrine)

This was also a thing. Discuss. If you feel inclined.

EP only comes to that conclusion when his star pupil became roasted, before that he fully believed Vader would eventually replace him. It's just that near death and limb loss is really bad for your total force potential.

Thing also to bear in mind is that like may real-world religions that rely heavily upon the belief of the participants to function, namely accepting various elements "on faith," is that the Sith Rule of Two or the Jedi Code start to fall apart when you apply heavy scrutiny and facts.

A good friend of mine in the past was a Catholic scholar, and fully admitted that if you applied scientific rationale and practical studies on actual human behavior as opposed to idealized human behavior, Catholicism as a whole doesn't really hold up. But as Delenn of Babylon 5 often said when faced with daunting prospects, "Faith manages."

How well it manages is up to the individual. I'm an atheist, so "faith" generally doesn't go that far for me. But for a bona fide believer in a higher power (such as the Jedi and the "will of the Force") or an established doctrine (Sith and the Rule of Two), "faith" goes a long way in making something that on paper shouldn't work or seem contradictory or silly, actually work better than maybe ought to.

Of course, there's always the Bellsario's Maxim and the MST3K Mantra, both of which are applicable when regarding the topic of fantasy/sci-fi religious structures...

The rule of two does indeed not make a lot of sense. Although it does make a slightly smaller amount of sense if you change Darth Banes motivations around a bit. The Sith ruin the galaxy whenever they start swinging big, they almost bring the republic to its knees before they start really get busy with the infighting. At that point they start using doomsday weapons against each other and each Dark Lord tries to amass as much power as possible, not to use against any external enemy but rather against internal enemies. This is pretty bad for the Sith and the galaxy as a whole. If you ascribe some altruistic motives to Darth Bane then it makes a bit more sense, the goal is to limit the damage the Sith cause to the galaxy.

If there are just two of them, and they work in the shadows rather than openly, then they're less likely to wreck entire sectors in internal power struggles. Now they're just likely to kill each other in their power struggle, with maybe some extras that one or the other bring to even the odds. A planet or two could get wasted, but not the wholesale slaughter of entire sectors through the use of doomsday weaponry.

Of course all of this is pretty daft speculation and doesn't really fit with his personality. And yeah, if you're seeking to preserve the Sith then the rule of two doesn't really make a lot of sense. Two people are too few to keep a legacy going, there are too many things that could go wrong. Even with Sith spectres running around the whole order should have ended after a few hundred years. If the goal was to preserve the Sith and weaken the republic, then Bane should have gone with Darth Krayts backup plan. Scattering and hiding the order among the republic, working individually or in small cells to build up a power base and weaken the Republic and the Jedi from within.