Puzzle: What is wrong with Mike?

PUZZLE: Mike works on the 9th floor of an under-constructed building. He always takes the elevator down to ground level at the end of the day. Yet every morning he only takes the elevator to the 7th floor and walks up the stairs to the 9th floor, even when is in a hurry. Can you think of some valid reason?

Solution & Explanation:

He is too short to reach the "9" button.