Five years ago, Brett’s 4-year-old son Nicolas went poking around his father’s closet and discovered several karate belts. He said, “Dad, I didn’t know you did karate,” Brett remembers. “I told him, ‘Yeah, 20 years ago,’ and he said, ‘You should be a white belt!’” Brett had, in fact, been considering a return to the dojo. When he went there for Nicolas’s classes, he found himself talking to the instructors and was intrigued enough to think about getting back into martial arts. At that point, Brett, who runs an international company, knew he was overworked, out of shape and about ...