You win, you win. You lose, you don't win.

Last Tuesday I played in a regional tennis tournament. I couldn't have asked for a better draw than the one I got. In my first round, the girl I was supposed to play was sick, so I got a buy. In the second round I had the opportunity to play someone who usually played 2nd doubles. Finally in the championship I was playing an old friend of mine from a summer league that I could easily beat. Then why did I lose!? When I was warming up, I was playing my best tennis. Then in the second round I was playing terribly, but luckily I still won. In the championship I was playing awful and so ofcourse I lost. After watching other people play tennis, and seeing myself winning all my region games and losing in the tournament, I've come to the conclusion that tennis requires more mental game than any other sport.
Tennis is the only sport in which it's just you against them. When you mess up, the only person there to blame is yourself. Other sports are never quite as individual and direct as tennis. In track, swimming, and golf, sure you're competing by yourself, but your opponent isn't right there in front of you immediately responding to all you do. And then to top that off, after every point you always have time to think about your mistakes or accomplishments.
Intimidation is another factor that heightens the mental game of tennis. Some people on my team who played doubles, once had the opportunity to play against this extremely intimidating girl. She was very tall ,muscular and blonde and she would wear a sweat towel on her head while she entered the court. Our team won , but it took a lot of mental ability for them to beat the "towel girl."I've even tried a little bit of intimidation on other people myself, and boy does it work. I used to play doubles over the summer and my partner and I would stand on the other side of the court and act like we were discussing the other teams strategies. Then we'd point at random places on their court as if they were weak spots or something. It worked. The other team would be focusing on those spots that we were pointing out and they would forget to focus on the game. We would also try grunting for each other, but I'm not sure that had the same effect. Also, mental game is such a big factor in tennis that on the video game Topspin, they've even included a button you can press after ever point called the "attitude now" button that raises your players mental ability. If you press it a lot, your player plays better and makes harder shots, just like you'd play in a real game with a good mental game.
The mental game of tennis is huger than any other sport's mental game. You can be physical and athletic, but you could never survive in tennis without a good mental game.