How did the instructor "build a swimmer" out of Douglas?

Explanation

The instructor worked gradually on Douglas' psychology, moved on to his physical movements and then integrated each part to build a swimmer out of him.
Initially, he made Douglas swim back and forth across the swimming pool so that he could get used to it. He used an elaborate mechanism with a rope, belt, pulley and an overhead cable to help them stay connected while Douglas was in the pool. Then, one- by-one, he made Douglas master the individual techniques of swimming, like putting his head in the water, exhaling and inhaling while in water, movements of his hands, body, legs, etc. Finally, he integrated these perfected steps into a whole experience of swimming for Douglas.