In January 1969, two quarterbacks played against each other in Super Bowl III. Johnny Unitas and Joe Namath were both superstars. They were both from western Pennsylvania, but they came from different cultural universes. Unitas was reticent, workmanlike and deliberately unglamorous. Namath was flashy and a playboy. He turned himself into a marketing brand and wrote a memoir jokingly called, “I Can’t Wait Until Tomorrow ’Cause I Get Better Looking Every Day.”

The contrast between these two men symbolizes a broader shift from a culture of self-effacement, which says, “I’m no better than anybody else and nobody is better than me,” to a culture of self-expression, which says, “Look at what I’ve accomplished. I’m special.”

The conventional story, beloved especially on the right, is that this cultural shift took place in the 1960s. First there was the Greatest Generation, whose members were modest and self-sacrificing, but then along came the baby boomers who were narcissistic and relativistic.

As I found while researching a book, this storyline doesn’t really fit the facts. The big shift in American culture did not happen around the time of Woodstock and the Age of Aquarius. It happened in the late 1940s, and it was the members of the Greatest Generation that led the shift.

The real pivot point was the end of World War II. By the fall of 1945, Americans had endured 16 years of hardship, stretching back through the Depression. They were ready to let loose and say farewell to all that. There followed what the historian Alan Petigny called “the renunciation of renunciation.” The amount of consumer advertising on the radio exploded. Magazines ran articles on the wonderful lifestyle changes that were going to make lives easier — ultraviolet lights that would sterilize dishes in place of dishwashing.

In 1952, Norman Vincent Peale came out with “The Power of Positive Thinking,” which rejected a morality of restraint for an upbeat morality of growth. That book rested atop the best-seller list for an astounding 98 weeks.

Then along came humanistic psychology, led by people like Carl Rogers, who was the most influential psychologist of the 20th century. Rogers followed the same basic line: Human nature is intrinsically good. People need to love themselves more. They need to remove external restraints on their glorious selves.

Humanistic psychology led to the self-esteem movement and much else, reshaping the atmosphere in schools, human-resources departments and across American society.

In short, American popular culture pivoted. Once the dominant view was that the self is to be distrusted but external institutions are to be trusted. Then the dominant view was that the self is to be trusted and external constraints are to be distrusted.

This more positive view of human nature produced some very good social benefits. For centuries people in certain groups in society had been taught to think too poorly of themselves. Many feminists and civil rights activists seized on these messages to help formerly oppressed groups to believe in themselves, to raise their sights and aspirations.

But I would say that we have overshot the mark. We now live in a world in which commencement speakers tell students to trust themselves, listen to themselves, follow their passions, to glorify the Golden Figure inside. We now live in a culture of the Big Me, a culture of meritocracy where we promote ourselves and a social media culture where we broadcast highlight reels of our lives. What’s lost is the more balanced view, that we are splendidly endowed but also broken. And without that view, the whole logic of character-building falls apart. You build your career by building on your strengths, but you improve your character by trying to address your weaknesses.

— David Brooks is a columnist for The New York Times. John Costa’s column will return.