You go back to check the front door not because you think you left it unlocked, but because you can’t remember locking it, which is a different problem. A door you lock every day gets locked so smoothly that nothing is written down: the hand does it, and memory is never asked. So you walk back, try the handle, and of course it’s locked. The trouble is that the check is a habit now too, and by the time you reach the corner you can’t quite remember that either. The usual advice is to make the moment strange: say “locked” out loud, or do something slightly silly with the key. It works for the same reason the forgetting happened. You remember the things you did on purpose, and almost nothing you did well.