What is the right answer?

A man lives on the 20th floor, and in the morning, he takes the elevator down to the lobby and goes to work. When he comes back home, he takes the elevator to the 10th floor and walks up to the 20th floor. Why?

He can only reach the 10th floor button on the panel since his is a short person

Thanks mxm. That was quick.

...but...but...not when it rains...
then he uses his umbrella to reach the "20th button"!

Very funny!