Dr. Gawande, MD, author, columnist for the New Yorker, gives a compelling explanation of why everybody needs a coach. He describes how sports taught the world that the journey for self-improvement never ends so even people like violin virtuoso Itzhak Perlman have coaches to help them see what they can't on their own.
Seymour Bernstein, a piano virtuoso in his own right and the subject of Ethan Hawke's documentary "Seymour: An Introduction", retired in his 50s to become a piano teacher for other virtuosos. If you haven't seen this doc, it is amazing!