As the former great Yankees' catcher Yogi Berra once said, "Baseball is 90 percent mental; the other half is physical." The same goes for tennis.
At the professional level, everyone can hit a solid forehand or ace someone on the serve. The difference is who can execute such shots under the pressure of competition. The ability to do so is called mental toughness.
Pete Sampras is one of the all time greatest tennis players. How did he get that way? Surely his serve and volley game contributed, but really it's all about his mental fortitude. Sampras was a subtle player in every aspect of the game. He didn't explode with emotion on court; but rather, Sampras was workman like in his style of play.
In a typical Sampras match he would trade service holds back and forth. Then, as he approached the end of a set, either up 5-4, or 4-3, he would turn up the intensity and try to break his opponent's serve. Assuming he would hold serve, Sampras figured that as long as he could get a break, then he could win the set. Guess it worked, because Sampras went on to become a world number one, and break the all time record for Grand Slam victories, winning a total of 14.
Rafa is one talented tennis player. Though a natural righty, his Uncle taught him to play tennis with his left hand, giving him a considerable advantage on the court. Nadal's biggest weapons are probably his topspin forehand and all around court coverage. But just like any great champ, the key to his greatness lies in his mental toughness.
For Rafa, it would be his ability to come back from the brink of defeat (either in a point, a game, or a match). Nadal has an uncanny ability to turn the tables on his opponents. No matter how much his opponent seems to have an advantage, up 40-0 in a game or 5-2 in a set, don't count Rafa out. He will come back from the edge of that cliff and regain the momentum.
Take a look at the epic 2008 Wimbledon final against Roger Federer. Nadal was up a set but then down 1-4 in the second. Playing against a quality opponent like Federer, one would assume that Nadal would lose the second set. Not the case. He pulled off five straight games to take the second set 6-4. Though Nadal was up by two sets, he lost the next two to even the match. While the momentum was now in Federer's favor, Nadal maintained his focus in the fifth set and held on to win in a dramatic 9-7 finish. Having a blistering forehand or a consistent serve is helpful, but it doesn't mean much if you can't play the big points well. Thankfully, Nadal has both.
Roger Federer may be the most talented tennis player the world has ever witnessed. He has a complete game—from his serve, to his power forehand, to his crisp volleys. In terms of stroke quality, Federer's game is unstoppable. However, that is not what makes Federer great. Instead, Federer's biggest weapon is probably his ability to remain calm, cool, and collected under pressure.
In 17 Grand Slam finals appearances, Federer has only lost four matches, and all four losses came at the hands of Rafael Nadal. Federer won five straight Wimbledon finals from 2003-2007 and five straight U.S. Open titles from 2004-2008. Those records speak volumes about the strength of Federer's mental game.
Except for the likes of Nadal, and recently Andy Murray, Federer's mere presence on the court seems to send shivers down the spine of his opponents. As soon as the mental battle begins, you can rest assured that Roger is winning the war. Roger Federer crushes his opponents because he knows that he is better. He plays to win, rather than playing not to lose. And that is the reason Federer is one of the all time greats.
While it is important to have talent, the most important factor to determine success is not physical ability. Rather, it is the mental capacity to will yourself to win. Of the three players discussed above, each one has great strokes. But hitting a solid forehand will not win a match. However, hitting a precision forehand on a pressure point will. The ability to turn on the gas when needed, come back from the brink of defeat, and have complete self-confidence is what breeds greatness.
Imagine this—it's your serve at 30-40, 4-5 in the final set. How will you play?