Hi {{first_name|there}}, it’s Thomas.

A few years ago, I was scrolling through old photos from a conference I attended nearly a decade ago (where has the time gone?!), and I stopped on a set of group shots that felt strangely distant.

There were dozens of smiling faces in those pictures—people I had shared meals with, laughed with, collaborated with, and promised, in that very sincere conference way, to “keep in touch.” At the time, many of them felt like permanent fixtures in my life, the kind of connections you assume will always be there in some form.

Today, I barely know where most of them live.

Some have become old, cold connections. Others have drifted all the way into complete stranger territory.

For a long time, I assumed something was wrong with me. I kept asking why certain friendships quietly faded, why groups that once felt like home no longer resonated, and whether I had simply failed at being a better friend, or whether everyone else had.

Eventually, the answer felt less like a personal failure and more like a pattern.

Friendships aren’t necessarily failing. They’re evolving.

A concept that’s been circulating online is the Five-Year Stranger Theory, which suggests that many of the people who feel central to our lives today may become strangers within five years, while people we haven’t even met yet will become some of our closest companions.

At first, that idea can feel a bit bleak.

But the more you sit with it, the more it starts to sound like something most of us have already lived through.

Think back five years, to when we were just emerging from COVID isolation.

Who were you seeing every week? Who filled your group chats, your lunch breaks, your gym sessions, your Saturday routines?

Now look at today.

Some of those people are still close. Many aren’t.

And in most cases, it isn’t because anything went wrong. It’s because life kept moving.

One of the most overlooked drivers of friendship isn’t compatibility; it’s proximity.

We become friends with classmates because we share classrooms. We become close with coworkers because we spend forty hours a week solving the same problems. We bond with neighbors, parents from our children’s schools, teammates, and volunteers because our lives keep overlapping in predictable ways.

Shared context creates repeated interaction, repeated interaction creates familiarity, and familiarity quietly turns into friendship.

Then the context changes.

Graduation happens. A new job appears. Someone moves across the country. Retirement begins. Children arrive. An empty nest follows.

And just like that, the structure that held the friendship in place disappears.

Without intentional effort, the relationship often starts to cool—not because anything broke, but because the environment that sustained it is no longer there.

This is where the research of Dutch sociologist Gerald Mollenhorst becomes especially reassuring.

His work found that while the overall size of our social networks tends to remain surprisingly stable over time (aka, Dunbar’s number), the people inside those networks change significantly. Roughly half of our close and meaningful relationships are replaced over a period of about seven years.

This pattern is what I refer to as Dunbar’s Churn.

And the key idea isn’t loss. It’s replacement.

We don’t stop building social wealth as we age. We just tend to build it with different people as our circumstances shift.

But there’s an important caveat here.

It only counts as churn if new relationships are forming to take the place of the old ones.

If friendships fade and nothing new is added, then it stops being churn.

It becomes shrinkage.

And that’s where many adults quietly find themselves.

One reason adulthood can feel lonelier than earlier stages of life is that we often become passive about making new friends.

When we’re younger, the system does a lot of the work for us.

School rotates in new classmates every year. College drops us into entirely new social ecosystems. Early careers place us into teams of strangers who slowly become colleagues, and sometimes friends.

Later on, that constant reshuffling slows down, and we tend to rely on whatever relationships already exist.

Meanwhile, life continues doing what it always does.

People move. Careers change. Families grow. Retirements begin. Friendships cool.

And if we aren’t intentionally refreshing our friendship pool, our social wealth doesn’t collapse all at once; it erodes quietly over time.

Not dramatically.

Just steadily.

One of the more freeing implications of the Five-Year Stranger idea is that not every friendship is meant to last forever.

Some people are companions for a specific chapter. Others stay for the long haul. Most fall somewhere in between.

And none of those outcomes, on their own, determine whether the friendship mattered.

We’re often taught to measure friendships by duration, as if anything that ends must have failed.

But a more useful measure might be contribution.

Did this person shape who you became? Did you learn something together? Did you laugh more because of them? Did you support each other through a meaningful season of life?

If the answer is yes, then the friendship likely succeeded, even if it eventually grew quiet.

Seeing it this way allows us to hold past relationships with gratitude instead of guilt, and it frees us to invest more fully in the people who are entering our lives right now.

Before next week’s newsletter arrives, take twenty minutes to do a simple inventory of your friendship portfolio.

Start by identifying one old or cold connection you’ve been meaning to reach out to. Send them a short message. No apology, no explanation—just a simple reopening of the door.

Then ask yourself a second question:

Where am I currently creating opportunities to meet tomorrow’s friends?

That might mean joining a community group, attending a professional event, volunteering, taking a class, or finally saying yes to an invitation you’ve been avoiding.

Because while losing friendships is part of being human, replacing them is part of building social wealth.

And your friendship portfolio was never meant to run on autopilot. Like any meaningful investment, it grows best with both careful maintenance and fresh contributions over time.

Do you subscribe to the five-year stranger theory? If not, do you have something you think could help others? Just hit reply — your email goes straight to my inbox. 🙏