MY TWO CENTS: The simple answer, he or she is not a pure athlete.  Your desire to win should prevent you from not giving everything you have each time you step on court.  However, nothing is ever that simple, so there has to be other reasons why so many gifted players never maximize their potential. It’s befuddling to watch a player that has every aspect of the game, struggling to consistently win tournaments and a major title.  If those were not your objectives, why then did you make the sacrifices to become a tennis player?  In an individual sport, the onus to succeed rests solely on your shoulders, no one can compete for you. If it is not winning titles,  what is the appeal to tennis?  Is achieving enough status to enjoy the glamour and fame of being a professional athlete the attraction?  You reap the benefits of being on tour and you enjoy the attention, so you do just enough; yet, you fail to realize that if you are not consistently competing and winning titles, you will lose your appeal.  Still, that cannot be the answer for everyone.  A more accurate response may be that the desire is there; however, the will is compromised by doubts and that’s why so many gifted tennis players never live up to their potential.