I wish I did double check. I've grown so accustomed to having certain things in certain places (apartment keys in jacket pocket), that I've started to just assume they are there, and not even bother checking. Cost me 20 euros once, and on another occasion, an hours wait for my roommate.
I used to like.. billion-check as a kid. There was never a point of no return for me as a kid. I lock the front door, leave for school, come running back after five minutes, just to make sure the door is locked, leave for school, come running back AGAIN, because it still for some reason might've not been locked.
Another Finn, woop!