Mistakes are not eliminated by constant practice unless you practice not making mistakes. If you just keep repeating yourself, you'll just learn to optimize around your mistakes and never reach peak performance.
Yes, but it is one thing to recognize and correct mistakes made in the course of practice -- allowing performance mistakes to haunt you is quite another. A player who derives less pleasure from his successes than disappointment from his failures has little reason to continue playing. Successful players focus on the positive.
This happens to musicians a lot.