One of the games key mechanics is your people can lose sanity and gain stress. At a certain point in a dungeon they can have their resolve tested. Either they shine, becoming heroic or courageous, or they will (more likely) break. Breaking causes them to be a take a random characteristic including paranoid, selfish, abusive and masochistic. This kind of result can seriously endanger any expedition you are currently engaged in, and can only be cured by sending them to drink, gamble or pray.

There's also more permanent mental conditions, positive or negative, that can only be fixed by sending them to the asylum

All in all it's a pretty bleak game