Only the feeling that there would always be another tomorrow.… When people look back on their student days, they tend to remember friendships in unusually warm colors. They remember the convenience-store runs after class, the cheap restaurants where nobody had enough money, the midnight conversations about careers and love, and the ridiculous jokes that somehow remained funny twenty years later. They rarely remember the small irritations. The unanswered messages. The friend who always arrived late. The classmate who quietly competed with everyone else. The person who borrowed money and never returned it. Those details gradually disappear because autobiographical memory is not a video archive. Research in cognitive psychology has shown that memories are reconstructed rather than simply replayed, and emotionally significant memories can become especially resistant to the ordinary erosion of time. When people repeatedly tell the same stories, the narrative can...