The Way of the Peaceful Warrior by Dan Milman

Olympic gymnast Dan Milman is mentored by an old grizzled garage attendant, like Nick Nolte. Socrates challenges Dan to a feat of true power and offers Dan the chance to go first. When Dan does 10 one-armed handstand pushups, he goes, oh, I went too far. And Socrates says, I noticed that there was a small buildup in my kidneys that would have become a kidney stone in about a month if I hadn't done anything about it. So I flushed it out with water.