How a Hot Dog Vendor Changed a Psychologist's Life

Opening

Reader, did you catch anyone’s eye this morning — on your commute, or at the corner convenience store?

A Canadian psychologist’s life was changed by a hot dog cart vendor she passed every day during grad school. She never once bought a hot dog, but every time she walked by, they smiled and waved at each other. That brief exchange gave a graduate student who was 10 years older than her peers and had started her program later in life the sense that “I belong here.”

That experience wasn’t just a passing anecdote. That psychologist, Gillian Sandstrom, went on to become a scholar studying how “weak ties” affect well-being, and what she found upended our conventional wisdom about relationships. The bottom line: happiness isn’t determined by how many close friends you have, but by how many different people you brush past in a single day.

🔬 The Surprising Power of Weak Ties — What the Research Says

In sociology, “weak ties” refer to relationships outside your “strong ties” — family, close friends, coworkers. The barista at your neighborhood café, the security guard at your building, the person who rides the same bus every day. People whose faces you know but whose names you don’t. Sociologist Mark Granovetter proposed the concept in 1973, originally in the context of job hunting and information diffusion — weak ties, he argued, were advantageous for both. But recent research shows these weak ties have a surprisingly large effect on psychological well-being too.

A 2014 study by Sandstrom and Elizabeth Dunn was the first social psychology research to systematically measure how weak ties affect happiness. The method was clever. More than 50 participants were given two click counters — one to press for every conversation with a close tie, the other for every conversation with a weak tie (acquaintances, strangers).

Over 6 days of tracking, participants were happier and reported a stronger sense of belonging on days with more weak-tie conversations. Crucially, this held up even after controlling for the effect of strong-tie conversations. In other words, people weren’t just happier because they talked to close friends a lot — weak ties functioned as an independent driver of happiness in their own right.

A follow-up study went even more granular. The researchers recruited 60 people outside a Starbucks in Vancouver. Half were told, “Order as efficiently as possible.” The other half were told, “Make eye contact with the barista, smile, and have a brief conversation.” The results were clear-cut. The group that talked with the barista reported more positive moods and a stronger sense of belonging. The coffee didn’t taste any different — a 30-second human exchange shifted the emotional tone of the entire day.

There’s an interesting paradox here. Most people predict that talking to a stranger will feel awkward and uncomfortable. But when they actually do it, they consistently report enjoying it far more than expected. Our brains tend to overestimate the cost of social contact and underestimate its reward. Sandstrom calls this the “prediction error of social contact.” In fact, Professor Kristin Jenkins at Cornerstone University in the U.S. had her students read this research and then complete an assignment: strike up a conversation with a stranger. Regardless of whether they were introverts or extroverts, the vast majority said they wanted to keep doing it.

🌐 Diversity Is the Answer — What Data from 50,000 People Shows

There’s research that takes this a step further.

A team led by Hanne Collins at UCLA analyzed data from more than 50,000 people across 8 countries to propose a concept called “relational diversity.” The central finding of this study, published in PNAS¹ in 2022, is this: the more varied the types of relationships you converse with in a day, the happier and more satisfied with life you are.

The study design was meticulous. It drew on a pre-registered survey of 578 Americans, 19,197 respondents from the American Time Use Survey, 10,447 participants in the WHO Study on Global Ageing, and 21,644 users of a French mobile app. The same pattern emerged across all four independent datasets — this wasn’t a single experiment, but cross-validation across more than 50,000 people.

What matters here isn’t the “quantity” of conversation but its “diversity” and “frequency.” Someone who talked only with coworkers all day was less happy than someone who talked with coworkers, a convenience store clerk, a delivery driver, and even sent a quick text to an old friend. Collins compares this to a “social portfolio.” Just as diversification matters in investing, diversity in relationships boosts psychological stability.

And this effect isn’t simply “socializing more felt good.” The research team confirmed that relational diversity was an independent predictor of happiness even after controlling for total time spent on social activity. In other words, even when people spent the same amount of time socializing, those who experienced diverse relationships were happier than those who focused on just one type.

What makes this study especially compelling is that the same pattern held across culturally distinct countries — the U.S., France, Ghana, India, China, and more. The link between social diversity and happiness transcends culture. Collins’s interpretation: contact with a diverse range of people creates a sense of “belonging to a larger social structure,” and that sense of belonging becomes a source of happiness.

🇰🇷 The Silence of 8.045 Million Households — Why Korea Is Especially Vulnerable

Place this research in the Korean context, and the picture turns fairly grim.

As of 2024, Korea has 8.045 million single-person households, 36.1% of all households. That figure has hit a record high every year since data collection began in 2015. Notably, single-person households aged 70 and older have outnumbered those aged 29 and under for 2 consecutive years — a marked rise in elderly single-person households. In effect, single-person living is converging into Korea’s future standard household form.

There’s an even more striking number. In a 2025 social survey, 48.9% of single-person households said they felt “lonely” — 10.7 percentage points higher than the overall household average (38.2%). This was the first time Korea’s National Data Agency surveyed loneliness among single-person households separately, and the scale of the result suggests just how much this problem has surfaced. The survey also found that 4 in 10 people nationwide say they generally feel lonely.

This loneliness isn’t just an emotion. According to the Ministry of Health and Welfare, 3,924 people died alone (godoksa, solitary/unattended deaths) in 2024 — a record high, up 7.2% from 3,661 the previous year. Among single-person households, only 68.9% said they had someone to help when sick, and 73.5% said they had someone to turn to when feeling depressed — both lower than the overall household average.

Add to this the fact that the WHO declared loneliness a “pressing health threat” in 2023, and the picture is complete. According to the WHO Commission on Social Connection, led by U.S. Surgeon General Vivek Murthy, chronic loneliness’s impact on health is comparable to smoking 15 cigarettes a day — a 32% higher risk of stroke, a 29% higher risk of heart disease, and a 50% higher risk of dementia. This isn’t a matter of emotion; it’s a matter of physical health. The WHO estimates that loneliness is associated with roughly 100 deaths per hour worldwide — more than 870,000 deaths a year.

But Korea has one more structural problem. For more than half of single-person households, the primary weekend activity is watching video content (75.7%). Instead of making eye contact with a barista at a café, they’re watching short-form videos on their phones in bed. Add the rise of delivery apps on top of that, and the physical opportunities for the kind of brief conversation with a restaurant worker, or a casual greeting at a convenience store, that Sandstrom’s research proved could deliver “30 seconds of human exchange,” are systematically shrinking.

🏠 What Remote Work Erased

One of the biggest changes brought by the COVID pandemic was the normalization of remote work. But while remote work boosted efficiency, it quietly took something away from us: weak ties.

The neighbor you ran into in the elevator on your way to work. The security guard in the lobby. The “what’s good today?” chat with the owner of the neighborhood gimbap shop at lunch. All of that disappeared. Video calls can substitute for work conversations, but they can’t replace a chance encounter in the hallway or small talk by the coffee machine. It’s hard to bring up “hey, did you catch that drama?” on a Zoom call.

A 2022 study of 1,511 Norwegian workers illustrates remote work’s double edge well. As remote work increased, loneliness at work rose significantly — but workplace bullying decreased at the same time. Bad relationships were blocked, but good ones, especially “weak ties,” disappeared along with them. A 2025 longitudinal study by a University of Hamburg research team also confirmed a trajectory in which longer periods of remote work were tied to a steady rise in workplace isolation.

Japan’s case is also revealing. A study analyzing 4,052 Japanese office workers doing remote work during the third wave of COVID found that people who worked from home more frequently scored significantly higher on loneliness than those who commuted to the office. Loneliness was worst among remote workers who lived alone — because for them, weak ties at the workplace had effectively been their only regular point of social contact.

What Professor Robert Waldinger, who has led the Harvard Study of Adult Development² for 85 years now, has to say resonates especially here. He says these small, everyday points of contact confirm our sense of belonging — the feeling of being recognized by others, something even the lightest touch can provide. The study’s conclusion — that relationship satisfaction at age 50 was the single strongest predictor of health at age 80 — shows that relationships aren’t merely “nice to have.” They’re a resource necessary for survival.

Oz’s Lens

Honestly, this topic hits close to home for me.

After starting my own business and working as an independent consulting firm, the number of people I talk to in a day dropped sharply. There were things I never noticed while working at a company. Casually saying “hang in there” to someone from another team as you pass in the hallway. Exchanging a nod with the person at the next table in the cafeteria. Arriving five minutes early to a meeting room and making small talk. All of that was weak ties.

Now I work at a monitor all day, and on some days, the “thank you” I exchange with the clerk at the convenience store in the evening is the only face-to-face conversation I have. Looking at Collins’s research, my own “social portfolio” has become extremely concentrated — in investment terms, it’s like putting everything into a single stock.

Something I’ve learned while building GTM strategy: people think big decisions change a life, but in reality, it’s the accumulation of small, repeated daily actions that drives change. A product doesn’t succeed in the market because of a big launch event — it succeeds because it repeatedly delivered small value to users at everyday touchpoints.

The same principle applies to weak ties. Rather than the grand prescription of “make good friends to be happy,” something like “tomorrow morning, look the convenience store clerk in the eye and say hello” is far more actionable — and according to the research, it actually works.

There’s one thing I want to flag, though. As beautiful as this research is, striking up conversation with a stranger remains a fairly high psychological barrier in Korean society. The natural culture of greeting strangers in the U.S. or Uganda doesn’t map directly onto the Korean context. So rather than “talk to strangers,” I think a more realistic starting point is warming up your contact with people you already encounter every day by just 0.5 degrees. Instead of just nodding at the security guard in your building, make eye contact and add a “have a good one.” That’s enough.

Closing

To sum up:

First, from the 85-year Harvard study to the latest PNAS paper, it’s settled science that social relationships are the strongest predictor of health and happiness. Second, what we’ve underestimated in those relationships isn’t “close relationships” but “weak ties” — the brief contact with the people we brush past every day. Third, Korea is a country of 8.045 million single-person households, where half report feeling lonely. Remote work and delivery culture are systematically eliminating weak ties.

Having read this newsletter today, why not try one thing tomorrow morning?

Whoever you happen to pass — a convenience store clerk, a building security guard, a café barista — hold eye contact 0.5 seconds longer than usual, and say something. Those 30 seconds might change not just their day, but yours too.

References & Further Reading

Primary sources

• Sandstrom, G. M. & Dunn, E. W., “Social Interactions and Well-Being: The Surprising Power of Weak Ties,” Personality and Social Psychology Bulletin, 2014. The first study to systematically measure the relationship between weak ties and happiness.
• Collins, H. K. et al., “Relational Diversity in Social Portfolios Predicts Well-Being,” PNAS, 2022. Uses data from 50,000 people to demonstrate the link between “social portfolio diversity” and happiness.
• Sandstrom, G. M. & Dunn, E. W., “Is Efficiency Overrated? Minimal Social Interactions With a Barista,” Social Psychological and Personality Science, 2014. The original paper behind the Starbucks barista experiment.

Background

• Waldinger, R. & Schulz, M., The Good Life: Lessons from the World’s Longest Scientific Study of Happiness, Simon & Schuster, 2023. A summary of the key findings from Harvard’s 85-year longitudinal study — essential reading for understanding why relationships are the strongest predictor of health and happiness. Published in Korea by Business Books under the title The Longest Study on Happiness in the World.
• National Data Agency (Korea), “2025 Statistics on Single-Person Households,” 2025. The original source of key statistics cited here, including Korea’s 8.045 million single-person households and the 48.9% loneliness rate. Note: Statistics Korea has been renamed the National Data Agency.
• WHO, “Commission on Social Connection,” 2023. The official document declaring loneliness a global health threat.

The author, Kwangseob Ahn, is a professor of business administration at Sejong University and lead consultant at OBF (Oswarld Boutique Consulting Firm). He teaches statistics and data analysis — business data management and business analytics — while leading GTM and AI strategy consulting in the field, designing the seam between technology and business. He has published academic research on a memory architecture for AI dialogue systems (HEMA) and runs Daily Arxiv, a daily curation of global AI papers. He holds a master’s from Korea University’s Graduate School of Technology Management and a KMBA. He is the author of Homo Brainless: The People Who Outsource Their Thinking.

Footnotes

1. PNAS (Proceedings of the National Academy of Sciences): A globally prestigious academic journal published by the U.S. National Academy of Sciences. It covers a broad range of fields from natural science to social science, and is ranked, alongside Nature and Science, among the top-tier journals. ↩

2. Harvard Study of Adult Development: The world’s longest-running study of happiness, begun in 1938 and now in its 85th-plus year. It originally started with 724 participants — Harvard undergraduates and teenagers from Boston’s poorest neighborhoods — and now tracks 1,300 of their children as well. It’s famous for its conclusion that “good relationships are the most important thing in life.” ↩