Flow

"Contrary to what we usually believe... the best moments in our lives, are not the passive, receptive, relaxing times—although such experiences can also be enjoyable, if we worked hard to attain them. The moments usually occur when a person's body or mind is stretched to its limits in a voluntary effort to accomplish something difficult or worthwhile. Optimal experience is something we make happen. For a child, it could be placing with trembling fingers the last block on a tower she has built, higher than any she has built so far; for a swimmer, it could be trying to beat his own record; for a violinist, mastering an intricate musical passage. For each person there are thousands of opportunities, challenges to expand ourselves."

"Such experiences are not necessarily pleasant at the time they occur. 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 from his book, Flow: The Psychology of Optimal Experience