Step 1: Analyzing the man’s behavior.
The man’s behavior suggests that he is a short person, possibly of limited height, who cannot reach the button for the 15th floor in the lift. Therefore, in the morning, he presses the button for the 10th floor and walks up the remaining floors. In the evening, he presses the button for the ground floor from the 15th floor.
Step 2: Conclusion.
The man is likely short in height and cannot reach the higher button on the lift, so he gets off at the 10th floor and walks up.