Love the tennis coach story and it reminded me of my teacher on my fundementals of programming course at college.
This caused up roar and complaints to the course head. However he was right at the end of the course out of 24 people, 12 had flunked out, 10 had moved to systems analysis and 4 of us got jobs as programmers.
I think part of being good at anything is listening to the right people and acting when they tell you your not doing right.