A forensicator lives on the 10th floor of a building. Every morning he rides down the elevator to the ground floor and leaves the building to go to his forensic lab. Every night he comes home after spending the day finding evil and gets on the elevator. If it was raining then he takes the elevator to the 10th floor. If the weather is good then he takes the elevator to the 7th floor and walks to the 10th floor using the stairs. Why does he do this?