In self-discipline one makes a "disciple" of oneself. One is one's own teacher, trainer, coach, and "disciplinarian." It is an odd sort of relationship, paradoxical in its own way, and many of us don't handle it very well. There is much unhappiness and personal distress in the world because of failures to control tempers, appetites, passions, and impulses. "Oh, if only I had stopped myself" is an all too familiar refrain.
The father of modern philosophy, René Descartes, once remarked of "good sense" that "everybody thinks he is so well supplied with it, that even the most difficult to...