According to BrainDen.com:
This is one of the more popular and most celebrated of all lateral thinking logic puzzles. It is a true classic. Although there are many possible solutions that fit the conditions, only the canonical answer is truly satisfying.)
A man who lives on the tenth floor takes the elevator down to the first floor every morning and goes to work. In the evening, when he 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?
On a rainy day or when there are other people in the elevator, when he comes back from work he walks up all the floors and does not take the elevator at all. May be so as not to make it wet or messy or because he does not want to be in a confined space with others or wants to avoid them for whatever reason. Other days he takes the lift to the seventh floor only, possibly because he fancies some exercise or may be the lift stops three floors short of his apartment.
Because he’s short. Unless he has an umbrella with him, or there is someone in the elevator to help, he can only reach the “7″ button.