From an on-line Interactive Fiction magazine issue from 2001 ... Dunno how I stumbled over this "If you're writing a story-game, the code should automatically unlock and open doors you walk through if you have the key; it's just tedious if it doesn't. But if you're writing a puzzle game, then the code definitely shouldn't - if a player has had to work like fury to get that key then let them have the satisfaction of getting to unlock the damn door with it. Otherwise it plays like the game is tapping its watch saying 'I've grown grey hairs waiting for you to get on and solve that! Can we hurry up, please?'"