Those who know me well, know that I am a big fan of Mihaly (formerly UoC) and his work on Flow (TED Talk: Flow, Secret to Happiness). He has been on the forefront of work around positive psychology, researching "experts", 10000 hour rule, Happiness/Achievement/Creativity and much more.
Csikszentmihalyi also found that intrinsically motivated people were more likely to be goal-directed and enjoy challenges that would lead to an increase in overall happiness. Great quote from him below. The following framework is at the heart of his work, around aligning Challenge and Skill Level. His work is a must read including (Flow: The Psychology of Optimal Experience)
“A person can make himself happy, or miserable, regardless of what is actually happening ‘outside,’ just by changing the contents of consciousness. We all know individuals who can transform hopeless situations into challenges to be overcome, just through the force of their personalities. This ability to persevere despite obstacles and setbacks is the quality people most admire in others, and justly so; it is probably the most important trait not only for succeeding in life, but for enjoying it as well. To develop this trait, one must find ways to order consciousness so as to be in control of feelings and thoughts. It is best not to expect shortcuts will do the trick. “ - Mihaly Csikszentmihalyi