It varies between what article you read but the majority of sports psychologists say that in any sporting event it is roughly 80% mental 20% physical. Apart from that they all agree that in any sporting event "having the mental edge" over an opponent has the overriding power to eventually dictate the final score. A recent game score is Spadea over Blake. Spadea has now won the last 5 matches against him. No doubt at all to me that Blake definitely has the game to beat him but was it having the mental edge that held him back? Hewitt uses mental tactics, oh yeah that childish "come on" is a mental tactic. Serena has "intimidation" and ego down to a fine art. Federer is a true champion but how hard would it be to have him as your next opponent? Imagine the mental game that precedes the actual game!