Edith Piaf, the diminutive French singer who could belt out a tune like nobody’s business, won acclaim for her song “Non, Je Ne Regrette Rien,” or “No, I Regret Nothing.” Most of us in adulthood probably don’t share that sentiment. Regret can sit on our shoulders like a paratrooper’s pack, weighing us down by the thoughts of prospects diminished and opportunities demolished. We reach the age of 35 and wonder if our single-minded pursuit of a career has ended the possibility of marriage. Or we look around and see many of our friends successful in their careers while we seem stuck in a job that brings neither wealth nor satisfaction. Or perhaps we regret the damage our vices have heaped upon us. Our alcoholism cost us our marriage. Our addiction to gambling left us poor as any pauper in a Charles Dickens novel. Our hot temper and boorish behavior have …