One recent December, at age 53, John Kralik found his life at a terrible, frightening low: his small law firm was failing; he was struggling through a painful second divorce; he had grown distant from his two older children and was afraid he might lose contact with his young daughter; he was living in a tiny apartment where he froze in the winter and baked in the summer; he was 40 pounds overweight; his girlfriend had just broken up with him; and...