The toughest opponent on the court is not the temperature or the conditions, and it is not the player across the net. The toughest opponent is self-doubt, the convincing negativity that makes you believe you cannot win. You have to believe you can win, no matter how improbable it may be. Self-doubt can be useful when it is a motivator, but if you do not control it, doubt becomes destructive. There is a long list of low-ranked players who have upset top ranked players, so intellectually we know that winning is statistically possible. However, when self-doubt creeps in, suddenly you are unable to toss the ball to serve, your racquet seems to weigh a ton and your feet will not obey your commands to move to the ball. You see it all the time; a lower-ranked player leads early against a higher ranked  player, but then collapses in defeat. What is the solution? Maybe it is as simple as playing tennis instead of thinking tennis. After all, you have been practicing for years and your muscle memory will prevail if you allow it to. If you let yourself think about winning, losing, or the rank of your opponent, chances are you will be catching an early flight home.  Tennis requires that you develop tunnel vision and short term memory loss. You have to be able to stay completely focused on each point and you have to forget the errors that you just made. It sounds relatively simple; however, it is not and requires that you practice developing your mental strength just as you do your physical strength.