In case after case, the magic formula is capacity for intimacy combined with persistence, discipline, order and dependability. The men who could be affectionate about people and organized about things had very enjoyable lives.

But a childhood does not totally determine a life. The beauty of the Grant Study is that, as Vaillant emphasizes, it has followed its subjects for nine decades. The big finding is that you can teach an old dog new tricks. The men kept changing all the way through, even in their 80s and 90s.

One man in the study paid his way through Harvard by working as a psychiatric attendant. He slept from 6 p.m. to midnight. Worked the night shift at a hospital, then biked to class by 8 in the morning. After college, he tried his hand at theater. He did not succeed, and, at age 40, he saw himself as “mediocre and without imagination.” His middle years were professionally and maritally unhappy.

But, as he got older, he became less emotionally inhibited. In old age, he became a successful actor, playing roles like King Lear. He got married at 78. By 86, the only medicine he was taking was Viagra. He lived to 96.

Another subject grew up feeling that he “didn’t know either parent very well.” At 19, he wrote, “I don’t find it easy to make friends.” At 39, he wrote, “I feel lonely, rootless and disoriented.” At 50, he had basically given up trying to socialize and was trapped in an unhappy marriage.

But, as he aged, he changed. He became the president of his nursing home. He had girlfriends after the death of his first wife and then remarried. He didn’t turn into a social butterfly, but life was better.