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. In a state of fear, you will never see yourself as potentially better than your opponent.
Fear of injury is another inhibiting factor.
Ironically, playing to protect yourself against injury often leads to it, because you're pulling up, not following through with movements and contracting your muscles irregularly. The same sort of protective training occurs in bodybuilding. The effects of a torn rotator cuff, a pulled hamstring or whatever injury you may have suffered, all tend to linger long after the injury is healed sufficiently to be trained again. Being careful is prudent. But being unreasonably careful will serve naught but keeping you from your goal.