The Psychology of Optimal Experience Mihaly Csikszentmihalyi
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A book by the inventor of the concept of flow, which is basically the sense of losing yourself in an activity. Though you may also lose yourself in a passive entertainment such as a movie, this probably isn't flow, which involves a sense of active learning and problem-solving. Generally flow tends to happen when you are working on something that you are good enough at that you don't experience a lot of frustration and self-monitoring, but also that isn't so easy that you can do it on autopilot. Notably, people who do more flow activities like practicing a musical instrument tend to be happier than those who consume lots of entertainment, though the people who do flow may imagine that the people being entertained are having more fun.