The term "flow" was coined by the positive psychologist Csikszentmihalyi in 1990, which refers to a state of blissful "selflessness" achieved by individuals engaged in an activity with concentration. Early Csikszentmihalyi interviewed people with different occupations or interests, such as mountaineering enthusiasts, musicians, dancers, painters, and asked them to describe their state of mind while doing their favorite activities/jobs.
The results found the following common points: Happiness doesn't know time—they seem beyond time; Concentrate - as if forgetting oneself and raster to vector conversion becoming one with the environment at the moment; The process is challenging, but it will still be completed without sleep or without food; Thinking of yourself as being at your best, performing "to the best of you." So he said that these people had entered a state of "flow" at that moment. Among our household names, Michael Angelo's process of painting Genesis in the Sistine Chapel in the Vatican and Einstein's study of The Theory of Relativity may well have been a state of "flow."
Even without any external reward (reinforcement), the individual is still willing to participate in the activity - this is an intrinsic motivation; The challenge of work is matched and proportional to personal ability. Plus, as shown in the figure below, a considerable degree of challenge and ability is the only way to achieve a "flow" state. As long as the two do not match, we will only feel apathy, boredom, or Anxiety. Csikszentmihalyi believes that "flow" is the source of our happiness. Because when we enter a state of flow, we leave all our worries behind and focus only on the activity.