" The swimmer’s muscles might have ached during his most memorable race, his lungs might have felt like exploding, and he might have been dizzy with fatigue—yet these could have been the best moments of his life. Getting control of life is never easy, and sometimes it can be definitely painful. But in the long run optimal experiences add up to a sense of mastery—or perhaps better, a sense of participation in determining the content of life—that comes as close to what is usually meant by happiness as anything else we can conceivably imagine. "

― Mihaly Csikszentmihalyi , Flow: The Psychology of Optimal Experience