The elevator in my apartment building is one of those old fashioned things with two sets of doors that open in opposite directions (one is in the stairwell, the other set is in the cage itself). You can't call it if it's already in service, you have to wait fifteen minutes for whoever is using it to finish before you can push the button. [Or you can stand there and push the button like an idiot even though the light is on, it just won't do anything.] There's no real air circulation, so if anyone smokes in there you smell it the rest of the day. Only three people can use if at a time (or four children), and even then it moves slower than cold molasses in January.
The Law of Elevator Function is this:
the more tired you are, the more frustrating your day has been, the less it is likely that the elevator will be there when you need it, or even be working at all.
More simply: elevator function is inversely proportional to the users existing level of frustration.