The Famous Elevator Puzzle

Riddle
Gogo the riddle Master  lives on the tenth floor takes the elevator down to the first floor every morning and goes to work. In the evening, when Gogo comes back; on a rainy day, or if there are other people in the elevator, he goes to his floor directly. Otherwise, he goes to the seventh floor and walks up three flights of stairs to his apartment.
Can you explain why?

    Gogo is a of short stature. He can't reach the upper elevator buttons, but can push is with his umbrella.