http://hallofbeorn.com/Cards/Details/Followed-by-Night-RtR

When Revealed: The first player (choose 1): deals 1 damage to all allies in play and Followed by Night gains surge, or all enemies engaged with players make an immediate attack, if able.

Can you "choose" to do something that can not happen, if there is an option that can happen?

You have some 1 health allies in play, but have no engaged monsters... could you still choose option 2?

You can choose either one in this case, because if there are 0 enemies engaged with players, "all" of them can make an attack, or if there are 0 allies in play, "all" of them can take 1 damage.

Here's a specific quote from Caleb (designer) about Followed By Night:

"When resolving any When Revealed effect that gives you a choice between two effects, you must choose an effect that you can fully resolve. Followed by Night is an odd example because you can always resolve either effect. That’s because it targets either ‘all allies’ or ‘all enemies’ and the word ‘all’ can include 0."

That's from this thread . So to recap: when choosing an effect, you have to do one that can be FULLY resolved. But because of how Followed by Night is worded, you are always able to FULLY resolve either effect.

this question gets asked quite often on the forums, you actually can choose either option because of the way the card is worded. Here are links to previous occasions that this has been discussed:

https://boardgamegeek.com/thread/783088/question-followed-night-encounter-card

https://community.fantasyflightgames.com/topic/126831-quick-question-followed-by-night/

Edit: Beaten to the punch by grandspleen by mere seconds... haha

what about other cards, not just Followed by Night... can you choose an option that doesn't resolve over one that will?

So to recap: when choosing an effect, you have to do one that can be FULLY resolved.

The answer applies to all choices. The only real answer is, "you have to choose an effect that can be fully resolved," as above. Pay attention to the wording in choices like that, because sometimes you can get away with selecting an effect that can be FULLY resolved and have no impact on the game state (like letting "all" enemies attack when there are 0 enemies in play). But if you have a choice between an effect that you can't resolve (like "remove 1 progress token" when there are no progress tokens in play) and one that you can, you have to choose the effect that can be resolved.

So the answer is yes.. you have to choose one that can resolve.

Thanks