A man who lived on the top floor of a twenty story building had to go up and down daily for work, and of course, for food and the other necessities. On most days he could only ride the elevator to the fifteenth story, and he would have to walk the rest of the way. When it rained, however, he could ride all the way up to the twentieth story. Why?
The man wasn't tall enough to reach the button for the 20th floor. He could only reach the 15th story button on the elevator. When it rained, he brought his umbrella, and used it to press the 20th story button on the elevator.