The problem here is that the man is actually a dwarf. The buttons in the elevator are arranged with the ground floor at the lower end of the panel, and the upper numbers at the top. The dwarf can only reach the numbers from the ground floor to the 30th, so he can go all the way down, but not all the way up. This problem can be extended by the statement that on a rainy day the man goes all the up to his floor in the evening. This is because on these days he carries an umbrella with which he can reach the higher numbers.