A man lives on the 10th floor of an apartment building. Every morning he takes the elevator down to the ground floor and goes to work. In the evening, he takes the elevator up to the 7th floor and walks the rest of the way to his apartment on the 10th floor, unless it has been raining that day, in which case he rides the elevator all the way to the 10th floor. The elevator works perfectly and stops at every floor. Why does he do this?
