I think one of the key flourishes of the game has to do with intrinsic vs extrinsic motivation. The game never presents a locked door where there is some key elsewhere, and the key goes into your inventory, and now you can open the door. At all times, all doors are openable. But you may not know the rules to the puzzle on the door yet. Once you learn them, the 'key' is knowledge and the 'inventory' is your mind.

If you're keen to this then you will find it surprising how few games work this way.