Good question at WhyNot.net: Why don’t elevator floor buttons come with undo? For example, when in an elevator and you press the wrong floor button why can’t you press it again and have the selection be un-selected? Similarly, if you’re at a landing and you somehow press “up” when you meant “down”, or vice-versa, why can’t you press said button again and have it turn off?
Granted, there are obvious issues. Impatient people like me press such buttons over and over again, mostly in a kind of totemic attempt to ritualistically convince the elevator that we’re in a hurry. Having an undo button that was over-sensitive would mean the elevator never really got going before the floor selection was turned off again.
Nevertheless, real-world systems that provide no support for undo-ing your selection should be the exception, not the rule. Humans are, if nothing else, over-eager to make decisions that they later want to change, and as such elevators should be no different than blgo^K^Kog entries.