As I approached the age of fifty, I felt a sense of unrest. I began to feel, I suppose, an uneasiness about whether I had accomplished or fulfilled my ultimate purpose for being on the earth. I was being plagued by a strong thirst for significance and a desire to make a difference, but not just any difference-a lasting difference. It was not retirement I was thinking about, though that is understandable coming up to the big five-O I knew it was not...