Self-mastery is the ability of an individual to control his or her life in accordance with his desired values and principles. It is one of the key factors to achieving happiness simply because happiness is dependent on following rules and guidelines.
For instance, if you want to feel good at having a healthy body, then you have to follow the rules of proper nutrition and dieting. If you want to get along with your co-workers, then you have to follow simple rules of good manners. Life, in more ways than one, is about following rules.
One reason why top athletes always hit their mark is because of the hidden reservoir of strength and endurance that they tap once they get the urge to give up. This is what is known as the second wind phenomenon. You run very fast and become short of breath that you feel like stopping, but you push yourself to go on and, after a while, you feel reinvigorated enough to pick up the pace.
How does this sudden recovery happen? Well, when you run so fast, your muscles require more oxygen than you can breathe. You develop an oxygen debt that causes pain and burning in your muscles, making you gasp for air. But when you slow down, you are actually working just as hard as you did when you were at a faster pace.
Eventually, you catch up on your oxygen debt and pick up the pace, not knowing that it was the slower running that reinvigorated you. In the same manner, all of us need to draw on this second wind if we ever want to achieve mastery of ourselves.