Jack Nicklaus, on the subject of golf, offered that fear, pressure and doubt are all part of the game. Jack noted that "if you don't feel them, you're already dead." Jack offered that "a champion is the one who manages them best." Interestingly enough, Jack was a strong believer in "selective memory," meaning remembering the good and blocking out the bad to the greatest extent possible, as an approach to managing them.
I think it's, more or less, the same in pool. The most fearless player I've ever seen over the glorious green felt is Jose Parica.