Elevator paradox

bestofwikipedia:

The elevator paradox is a paradox first noted by Marvin Stern and George Gamow, physicists  who had offices on different floors of a multi-story building. Gamow, who had an office near the bottom of the building, noticed that the first elevator to stop at his floor was most often going down, while Stern, who had an office near the top, noticed that the first elevator to stop at his floor was most often going up. At first sight, this created the impression that perhaps elevator cars were being manufactured in the middle of the building and sent upwards to the roof and downwards to the basement to be dismantled.