" When you are faced with a challenge that is far beyond your skills, the result is anxiety. When your skills are high but the challenges are low, you are bored. If you have low skills and the challenge is also low, you are able to do the job but are unlikely to become absorbed in it—apathy is the characteristic response. But when the skills are high and in balance with a stiff challenge, flow occurs. It is the Aristotelian principle on a two-dimensional plot. "

― Charles Murray , Human Accomplishment: The Pursuit of Excellence in the Arts and Sciences, 800 B.C. to 1950