There should be some circumstance in which keys break, in order to solve the problem where you only ever need 1 key in the whole game. Perhaps a cursed key would have a chance of breaking when you try to use it.

However, this should not go the SLASH’EM route of allowing any unlocking device to break, since that just makes the player carry around extra keys. Skeleton keys should be made of bone and can break. Perhaps add a new key that is not breakable but is rarer than skeleton keys (stealing some of skeleton keys’ probability).

Lock picks and credit cards should possibly be able to break too.