Concentrating your effort on one or at most a few goals at a time increases the odds of success. Focusing on success is important because willpower can grow in the long term. Like a muscle, willpower seems to become stronger with use. The idea of exercising willpower is seen in military boot camp, where recruits are trained to overcome one challenge after another.
In psychological studies, even something as simple as using your nondominant hand to brush your teeth for two weeks can increase willpower capacity. People who stick to an exercise program for two months report reducing their impulsive spending, junk food intake, alcohol use and smoking. They also study more, watch less television and do more housework. Other forms of willpower training, like money-management classes, work as well.
This is relevant for sports because one of the deliverances of common sense seems to be that participating in sports, which is one way to exercise, is or at least can be conducive to moral growth. A kid might grow in courage as she faces adversity on the soccer field and then become more courageous in other areas of her life. While some studies show that very little of this is actually going on in sports, I would speculate that this is not because the potential is not there, but rather it is because we are not doing what it takes to realize the potential of sport for moral growth. In the above quote, it looks as if increased willpower just happens. The difficulty is that a person can demonstrate incredible self-control and discipline in one area of life, such as the diet and training regimens of elite athletes, but severely lack it in other areas, such as finances or relationships. The important question is how to expand a virtue from one realm of life to other realms. Or, to put it differently, how to develop a virtue such as courage or self-control so that it permeates more and more of my life, and not just my sporting life. Perhaps the practical lesson is that I should seek to develop a virtue like self-control in my sporting life, and then turn my attention and seek to develop it in another realm or two (such as reading, or eating, or in dealing with difficult people, or not watching tv).