This article is by Lee Seong-bong and read by an artificial voice.

"Do you think your appearance, clothing and mindset are younger than your age?"

When this question was posed to 852 men aged 35 to 60 working in Seoul and Gyeonggi, 81 percent said yes - they believed they looked younger than they really were. Only 15.6 percent thought they looked older, and a mere 3 percent said their appearance matched their age.

The study was conducted in 2011 by Kwak Keum-joo, professor emeritus of psychology at Seoul National University and distinguished chair professor at the Daegu Gyeongbuk Institute of Science and Technology.

Kwak, a developmental psychologist, described this as a kind of "positive illusion."

"Most people in middle age tend to believe they're younger than they actually are," she said.

Fourteen years later, that "illusion of youth" has taken on a new name: "Young 40," as it's called in Korea. When the term first appeared a decade ago, it was used admiringly to describe middle-aged people who were stylish, health-conscious and culturally savvy.

Today, however, the meaning has shifted. It often refers, with a hint of mockery, to those who try too hard to appear young - middle-aged men in trend-driven clothes or those seeking the approval of younger women, sometimes derisively nicknamed "Sweet Young 40s."

The JoongAng Ilbo sat down with Kwak to explore the psychology behind the Young 40 phenomenon. Why do people in their 40s still see themselves as young? Why do younger generations react so negatively to them? And how can today's middle-aged men and women navigate the awkward limbo between youth and aging with confidence?

'The 40s are the changing season of life'

Q. The term "Young 40" started as a compliment but has become a punchline. Why?

A. Think back to your first year of college. Even students just three or four years older - the returning upperclassmen - seemed much older. So, while people in their 40s today may look younger thanks to medical advances and health management, they still appear 'old' to those in their twenties. Some even call them "Teul 40," a portmanteau of teulddak, a slang term mocking the elderly, and "Young 40."

Forty-somethings, meanwhile, still think of themselves as young. That clash in perception creates tension between generations.

Why has buying trendy clothes also become something people make fun of?

Humans instinctively divide the world into in-groups [a group where a person identifies as a member] and out-groups. That tendency is becoming stronger - not just generationally but socially and culturally. In the past, Koreans often identified by region, such as Yeongnam [Korea's southeast] or Honam [Korea's southwest]. Now, they even draw boundaries by neighborhood or apartment brand.

The stronger one's group identity, the greater the hostility toward outsiders. For people in their 20s, those in their 40s are the out-group. They have their own cultural markers - fashion, brands, entertainment. When middle-aged people with more spending power start imitating those markers, young people often respond with ridicule.

Does the social climate play a role in this shift?

Yes. The Young 40s generation spent their twenties in the 1990s - the so-called Generation X. They were more individualistic and consumption-driven than previous generations, and they entered adulthood during an era of rapid economic growth and rising real estate values.

Today's twentysomethings, on the other hand, are growing up in a low-growth society. From their perspective, people in their 40s already had their share of prosperity. So when they see those same people now trying to "take over" youth culture - fashion, gadgets, entertainment - they feel resentment.

You've taught college students for a long time. What changes have you observed?

I've been teaching a course called "The Shaky 20s" at Seoul National University since 2005. Each semester, I ask my students, "What's the most important thing in your life?"

Before 2011,...