Self-esteem can vary greatly within the time confines of a single training session, and it can mean the difference between winning and losing in a competition setting. One minute you may hate yourself over an error you've committed on the posing platform or in the gym, and a few moments later you could reverse that feeling completely by performing exceptionally. However common this sort of scenario may be, it is not the sort of thing to be sought after. It would be far better if your self esteem going into the gym or competition was such that ONLY superlative performance throughout was possible. Day after day, month after month, building ONLY the possibility of success into your training by careful, integrated application of science will tend to maintain peak mental attitude and feelings of self esteem.
Success begets success.
For every winner, there are many losers, and often the distinguishing feature between the two is attitude, positive thinking and the absence of inhibiting fear. Fear of the competition, for instance, can put you in a defeatist frame of mind even before the competition begins. Instead, your goal is to foster belief in yourself, train hard to achieve the means to victory, then realize you have made your belief work for you. All your success comes first out of belief in yourself. In fact, belief and success go hand in hand.