Why do players do the things they do? I've got a fairly good group of players right now, but even they fall into a few rather extreme trends. The first trend I've noticed is that they tend to go for extreme overreactions, especially in anything that might become violent. A few examples:
1) The PCs find a freighter idling on the ground near the site of what has, so far, been a non-violent adventure site. They elect to 'disable it' just to be sure it can't become a threat later or be used as an escape route for anyone that might become a threat later.
2) The characters are involved in a brawl where non-lethal punches and kicks are flying. One PC (of six) goes down and suddenly this is seen as a green light to start pulling blasters - not to threaten, but to begin gunning down every opponent on lethal setting.
Applying logical outcomes to behavior like this will usually involve dead PCs in a short time, and that's likely not too satisfying, but letting the PCs act like total psychos (they're getting worse right now, not better) isn't either.