I went to the hospital today for some check-ups. The elevator opened on one of the floors. Nobody was there. It stayed open for a few seconds, closed, and we all moved on.
When I was a kid and this anomaly occurred, I used to think that it was caused by ghosts. Ghosts had pressed the up/down button, ghosts were standing there when the doors opened, ghosts entered the elevators and stood among us. Ghosts had places to go; how else were they going to get there? Take the stairs?
I believed this because I thought it was the most reasonable explanation. Even though it would render me completely useless as an adult, I still sometimes wish I had that kind of kid logic. Couldn't have been that somebody got sick of waiting and took the stairs. Couldn't have been that somebody accidentally pressed the wrong floor. Ghosts just have places to be, other ghosts to meet. The end.