Good sibling relationships loomed especially powerful: 93 percent of the men who were thriving at age sixty-five had been close to a brother or sister when younger. “It is social aptitude,” wrote George Vaillant, who directed the study for three decades, “not intellectual brilliance or parental social class, that leads to successful aging.” Asked what he had learned after thirty years of studying the cohort, Vaillant was clear: “That the only thing that really matters in life are your relationships to other people.”
