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No complex proof is required to show that doing something requires effort. Doing something well requires lots of effort, and doing things superlatively requires years of dedication for all but the few who are just wired differently. Such effort is always a combination of the mental and physical; emphasis more on one than the other, depending on the circumstances. Most people, surprisingly, are pretty willing to exert great physical effort. Mental effort is much less often greeted with enthusiasm. Why this should be is somewhat mysterious.