Mihaly Csikszentmihalyi’s 1975 foundational text, "Beyond Boredom and Anxiety," introduced the concept of "flow"—a state of optimal experience resulting from a balance between high challenges and high skill levels. Based on studies of intrinsically motivated activities like chess and surgery, the work outlines characteristics of flow, including intense concentration, a loss of self-consciousness, and altered time perception. You can find more details or an academic abstract on ResearchGate . Amazon.com: Beyond Boredom and Anxiety: 9780875892610