Want to keep your brain busy? Do a puzzle.

A man lives on the tenth floor of a building. Every day he takes the lift to go down to the ground floor to go to work. When he returns he takes the same lift to the seventh floor and then walks up the stairs to reach his flat on the tenth floor.

He always carries an umbrella even if it’s not raining. There is nothing wrong with the elevator or the building. He hates walking.

Why does he do it?