Pete Sampras
I can’t stress how important it is to train yourself to seek clarity at moments of doubt. You have to stay calm and have complete faith in your abilities.
-- Pete Sampras
For the record, it is probably easier for Pete Sampras, a tennis player who ranks among the top two or three in history, to have faith in his abilities than almost anyone else. That being said, what he's saying here can help players unlock what ability they do have. The key phrase here, "train yourself to seek clarity in moments of doubt," is extremely powerful stuff and deserves to be broken down. I'll take the second half of this first..."seek clarity in moments of doubt."
Clarity is especially desirable because it is efficient; when we think clearly, we don't waste time with anything inessential. Most performers have, at some point, found themselves in a few moments where every decision was easy, where they perceived and acted without hesitation. Most descriptions of the proverbial "zone" contain an element of this highly evolved decision-making. Sampras contrasts clarity not with "confusion," but with "doubt," a word that is not an exact opposite.
What I think he's after is the idea that decisions must be made under stress, and time and energy cannot be wasted on doubt. Only through commitment can clarity be achieved because any plan is much more likely to be successful if there is full commitment to it. In fact, by going on to say that the key is to "stay calm and have complete faith in your abilities," he's further stating the importance of commitment.
The first half of this quote is also telling: "...train yourself to seek clarity." Here, Sampras acknowledges that committing to a plan can be riskier than avoiding one. By committing, you have to take responsibility for the outcome. Some people are averse to this, and will only commit when they feel strong. Sampras believes that it's important not only to commit when you're feeling weak, i.e. in moments of doubt, but to practice doing so in order to be better at it. It makes sense: we have to get practice at committing in order to be able to feel comfortable doing it when we need it most.
Pete Sampras was one of the very few greatest male tennis players ever. He had a reputation as a player who played very well in important close matches, and players talked about him "raising his game" at the most important moments. I think that this quote shows a lot about his approach to these moments. He had trained his thoughts to be uncluttered, especially by doubt, which freed him to put his best foot forward at the most important times.