Flow Theory is common within Art Therapy. Mihaly Csikszentmihalyi first described it in his book The Psychology of Optimal Experience as “a perfect immersive state of balance between skill and challenges”.

Psychological Flow captures the positive mental state of being completely absorbed, focused and involved in your activities at a certain point in time, as well as deriving enjoyment from being engaged in that activity.

“My mind isn’t wandering. I am not thinking of something else. I am totally involved in what I am doing. My body feels good. I don’t seem to hear anything. The world seems to be cut off from me. I am less aware of myself and my problems.

“…being completely involved in an activity for its own sake. The ego falls away. Time flies. Every action, movement, and thought follows inevitably from the previous one, like playing jazz. Your whole being is involved, and you’re using your skills to the utmost.”

Mihaly Csikszentmihalyi
https://positivepsychology.com/mihalycsikszentmihalyi-father-of-flow/

Optimal Flow is the combination of the participants having the right level of challenge for their skill sets, where the skill is neither too tough nor too easy as to be boring, and having unambiguous short-term goals to receive instant feedback on the progress.

“Participants describe being ‘in Flow’ as a highly pleasurable experience. They enjoyed being in control of the task, related largely to the ongoing feedback they received. Ultimately, they found whatever they were doing to be highly self-rewarding.”

Stavrou et al., 2015
https://positivepsychology.com/what-is-flow/