I can name you a long list of failures at the Professional level of Tennis.
First to me is Nastase who though he won many tournaments and matches could have probably won many more were it not for his antics. His talent seemed unlimited.
Then comes Rios who fell to his demons before he actually won a slam but had already shown that he could dominate men's tennis after achieving number 1.
On the women's side, I see fewer examples but Capriotti comes to mind as a talent that was wasted for most of her career. At least she proved that she had it later, much later, but all of that time was missed in between.
Now we have more on the men's tour who again have physical mastery of the game but lack the discipline to hold off their demons that invade their thoughts and come out in the form of bad behavior. Some make excuses that tennis isn't important to them anyway so as a way for the ego to justify this failure pretend that it doesn't matter. Think Kyrgios. He has unbounded talent but lacks the discipline to hold his bad thoughts in check when faced with a challenge on the court.
Here is a comment by Ken Rosewall on the subject. Rosewall was a master of the game and self-control and I never noticed anything but a gentleman on the court when he played no matter the outcome. It's hard not a admire a person of such worth not only to our sport but to civilization.
