The custom of working earnestly at self-improvement through a series of exercises done every day, exercises which involve the body as well as the mind, is somewhat frightening to lazy people, somewhat impracticable to busy people, and somewhat superhuman to average ones. This is why so many of those who start any regime of regular exercises fail to continue and finish the course. The longer the daily period required, the sooner their enthusiasm wanes. Only those succeed who have exceptional determination and unusual persistence. The fact is, we are not easily amenable to rigorous discipline. But if the period of daily work were limited to essentials for a few minutes only, many more people would remain faithful to it.
-- Notebooks Category 5: The Body > Chapter 5: Exercise > # 16