A man lives on the tenth floor of a building. Every morning he takes the elevator down to the lobby and leaves the building. In the evening, he gets into the elevator, and, if there is someone else in the elevator - or if it was raining that day - he goes back to his floor. Otherwise, he goes to the seventh floor and walks up three flights of stairs to his apartment. Can you explain why?
This one's a bit of a groaner but a lot of fun when you know the answer.