You're continually testing your skills with steadily-increasing difficulty. You have an inherent yet self-imposed objective (to beat your own score or someone e

You're continually testing your skills with steadily-increasing difficulty. You have an inherent yet self-imposed objective (to beat your own score or someone else's). It requires high concentration but allows you to run on autopilot. It's textbook Flow Theory. See: http://en.wikipedia.org/wiki/Flow_(psychology) http://en.wikipedia.org/wiki/Flow_(psychology) Also Raph Koster's book A Theory of Fun