He answers:

"The hardest part is deciding what the algorithms are, and then simplifying them as much as you can. It’s difficult to get things down to their simplest forms. You have to simulate in your mind how the program’s going to work, and you have to have a complete grasp of how the various pieces of the program work together. The finest pieces of software are those where one individual has a complete sense of exactly how the program works. To have that, you have to really love the program and concentrate on keeping it simple, to an incredible degree."

This line alone demonstrates he was a good coder.