Flow is the state of complete immersion in a task, where effort feels effortless, time distorts, and the work itself becomes its own reward. Mihaly Csikszentmihalyi developed flow theory through decades of research, interviewing artists, athletes, surgeons, and chess players about the conditions that produce their best work. His 1990 book "Flow: The Psychology of Optimal Experience" laid out the requirements: clear goals, immediate feedback, and a precise balance between the challenge of the task and the skill of the person doing it. Too easy and the task becomes boring. Too hard and it becomes anxious. Only in the narrow band between the two does flow become possible.