What is the theme in Flow by Mihaly Csikszentmihalyi?

Another theme to consider is personal choice. Much of a person's happiness or discontent is achieved through personal choice. Every day people make choices that affect them both internally and externally. One person may choose to go to work while another decides that he's fed up and stays home. One person may train for a marathon, while another plans a bank robbery. With all judgments aside, personal choices can determine the level of happiness one experiences. Continued personal choices, good or bad, may be shape a person's life in a way one never could have imagined. Flow shows how a person may rethink personal choice in order to make the decision that is most likely to bring joy and fulfillment.