Wonder no more. The book has had a lasting effect on me, and the concept of flow has worked itself deeply into my thinking. This page explains the basic idea of flow, and touches on some of the reasons it's a powerful concept. It is a surprisingly deep question, considering all the varieties of fun.
Some people enjoy painting, others rock climbing.
Some enjoy whittling, others hiking. As it turns out, there indeed are. When Csikszentmihalyi interviewed all the kinds of people listed above, he discovered a common thread to their stories. The following is taken from his book The Evolving Self , pages xii-xiv, and is hopefully brief enough to be readable yet long enough to explain the key idea. It seemed clear that what was so enthralling about painting was not the anticipation of a beautiful picture, but the process of painting itself.