Why self-expansion is the key to long-lasting love and friendship

Think back to the great loves of your life and you may remember a heady time when each day seemed to sparkle with new possibilities. It was as if you were reborn and looked at yourself and the world around you with new eyes – a dizzying metamorphosis that was as delicious as it was unsettling.

I’m not just sentimental. A growing number of psychological studies show that our best relationships, whether platonic or romantic, are characterized by an exhilarating sense of growth. We fall in love with people who broaden our horizons and help us become a better version of ourselves. And if we want our love to last, we have to work hard to continue to maintain that growth.

This idea – known as self-expansion theory – is the brainchild of Arthur and Elaine Aron, husband and wife researchers at Stony Brook University in New York, who first proposed it in 1986. In the mid-1990s, they asked students to answer the open-ended question “Who are you today?” using as many words or expressions as possible. As expected, many students began dating during the study period, and when this happened, they began to use much more distinct terms in their descriptions: their understanding of themselves literally expanded, as their partners helped them discover new aspects of themselves.

Such changes were also apparent in formal psychological questionnaires. Students in the budding relationships began to develop greater self-esteem, which reflects a feeling of self-worth, and greater self-efficacy, which reflects someone’s perception of their own abilities.

Research on self-expansion has only accelerated over the past decade, with a series of studies examining the concept among diverse populations, such as members of the LGBTQ+ community. In each case, feelings of personal growth were accompanied by greater passion, greater commitment, greater sexual desire for their partner, and greater relationship satisfaction.

It can even determine the longevity of a couple. There are many possible reasons for ending a relationship, but Brent Mattingly of Ursinus College in Pennsylvania and colleagues showed that young couples with higher levels of personal expansion at the start of the study were less likely to consider a breakup over the next nine months. Meanwhile, other research has shown that, in contrast, people who experience low levels of self-expansion are more likely to think about cheating.

The effects of self-expansion can even be seen in the activation of our neurons, according to a study by researchers at Renmin University of China published two years ago. Over a seven-month period, they found that people who experienced greater personal expansion produced higher levels of synchronization with their partner’s neural activity. Literally, they were more likely to think on the same wavelength.

How you and your partner can grow together

Couples can encourage personal expansion in several ways. Through conversation, they introduce each other to new ideas and ways of seeing the world that may not have been apparent before, and their mutual encouragement helps each overcome challenges that might have previously seemed unthinkable. You might never have considered writing a novel or founding a start-up, for example, if your partner hadn’t pushed you to pursue your dreams.

As a couple’s lives become intertwined, they may even come to view themselves as a single entity with pooled resources, so that our partner’s talents — like creativity — begin to feel like ours. This is called “the inclusion of the other in the self” – and it is actually another form of self-expansion. If my partner is artistic, I might consider myself a little more creative through the simple association; my concerns about climate change could lead them to become more environmentally aware. We would both discover new aspects of ourselves that weren’t obvious before.

Finally, there are our shared experiences. As a couple, we may take up new hobbies or travel to new places that we had never tried before we met.

Each of these facets can offer advice for stoking romantic feelings and keeping that flame burning for the long term. For example, we can make our conversations as deep and meaningful as possible, so that we discover more about each other and ourselves. It’s no coincidence that the Arons also developed the “36 Questions to Fall in Love” which created a viral buzz. New York Times column. In the original studies, participants were assigned strangers and offered a series of talking points designed to encourage greater self-disclosure, such as:

• Do you have a secret intuition about how you will die?
• What, if anything, is too serious to joke about?
• What is your most precious memory?

In less than an hour, couples discussing these themes report greater intimacy than those who engage in more bland chatter. (You can read more about this here, on the University of California, Berkeley’s excellent Greater Good in Action site.) This may seem more difficult to do in established relationships, but research suggests that we often overestimate our knowledge about the people closest to us — and we might be surprised by what we discover if we simply take the time to find out what they really think and feel.

Second, we can spice up our time together by exploring new places or trying new activities that we’ve never tried before. In a series of studies, Cheryl Harasymchuk of Carleton University in Canada and colleagues asked people to document their lives with their partners and their feelings about them. They found that the more exciting or unusual their evenings were, the more they felt a sense of personal expansion and the closer they felt to their lover – and the greater their sexual desire for each other. There is no simple recipe. For some, it might be wine tasting; for others, stargazing or caving. Find a new experience that pushes each of you out of your comfort zone.

Although research has largely focused on the benefits of personal expansion for relationships, you can also enjoy some of these benefits by flying solo. In 2024, Emine Yücel of Selçuk University and Duygu Dincer of Istanbul Aydin University, both based in Turkey, showed that personal expansion can enrich our platonic friendships. Some people may even prefer to engage in self-expansion on their own. Expanding your view of yourself and your abilities will be exhilarating in itself, with or without a partner to encourage you.

Regardless of your relationship status, you might start opening your mind to new opportunities this Valentine’s Day. If you have a loving partner who can share the experience, all the better – but you don’t need to wait for “the one” to start.