Sport has a good impact on the personality structure. Dynamism, trusting, control, humility... are a little part of the advantages to regularly practise a sport.
The psychological balance is fundamental in a performance search because motivation and willingness is the key of success.
In fact, during strong and intense effort, it is important "to positive the suffering" to succeed to surpass oneself.
Several studies have shown that the belief in success bring success and inversely the fear in failure bring failure.
External references (coach, friends, etc.) play an important role on the psychological plan. These persons are able to influence (positively or negatively) the mental energy which is necessary to surpass oneself.