Cam and Dan Beaudoin’s three-decade-old problem began when they were kids. Dan would follow his big brother around. Cam, who’s about three years older, would distance himself. Dan would get mad; Cam would get mad back. Although their mom assured them that they’d be “best friends” some day, nothing much changed—until about three years ago, when a fight got so bad that the brothers stopped talking to each other completely. Dan left all of their shared group chats and unfriended Cam on LinkedIn.

But the brothers, who didn’t speak for about a year and a half, started to understand the gravity of this separation: They were on track to live the rest of their days apart, silently stewing. Dan reached out to Cam, and he told me they agreed: “We don’t want to be in our 70s and 80s wishing we had a relationship.” So they tried something that most siblings never do: They decided to go to therapy together.

Sibling therapy is a relatively unusual practice, which is perhaps surprising considering how common childhood sibling conflict is. It’s so common, in fact, that many siblings assume that the relationship will work itself out naturally. But sometimes it doesn’t. And the tenor of the bond can affect people for their whole lives, either protecting them through hardship or leaving them vulnerable to it. One study tracked participants for 30 years and found that closeness with a sibling in childhood (but not with a parent) predicted their level of depression by age 50. Another concluded that the warmth a subject felt from their sibling at age 23 predicted lower levels of depressive symptoms in middle adulthood, while the hostility they felt predicted anxiety and depressive symptoms. A sibling relationship “is like a shadow on us,” Geoffrey Greif, a University of Maryland School of Social Work professor and co-author of Adult Sibling Relationships, told me. “It is one that always is there, whether it’s the most wonderful relationship in the world or the most troubled.”

Still, psychologists tend to overlook the influence of siblings. Roughly 80 percent of Americans have at least one, but a 2012 review of literature between 2008 and 2018 found that fewer than 3 percent of close-relationship studies looked at sibling ties. Most of the research focuses on parent-child bonds, spouses, or peers, Shawn Whiteman, a Utah State University researcher who co-authored that paper, told me. And few resources or training materials exist for clinicians who might be interested in sibling work; as a result, few practice it.

But when I spoke with clinicians who do, they told me that sibling relationships seem to be getting more public attention. Erin Runt, a therapist who works with siblings, thinks that despite the recent increase in family members becoming estranged—or perhaps in response to it—a counter-impulse is brewing: a realization that severing a painful connection doesn’t always end in healing. “We have a generation of people who are more and more interested in repairing relationships,” she said. Perhaps they’re just accepting that as hard as they’ve tried, they still haven’t outrun the shadow.

Many people think of parent-child relationships as the most formative ones—the source of attachment styles, daddy issues, tragic flaws. But siblings tend to model how to interact with peers, to share and to compromise (or not), to fight and make up (maybe). They’re the ones who can make a difficult home situation much better or much worse, Runt told me. They form their identities in relation to each other: what the other excels at or struggles with, how others—perhaps, especially, parents—compare them. And siblings compete for resources growing up. “You’re kind of always assessing,” Runt said. “What are they getting versus what I’m getting? How am I treated versus how they’re treated? What version of Mom or Dad or other family members are they getting, versus what I get?”

Karen Gail Lewis, a Washington, D.C., therapist and the author of Sibling Therapy: The Ghosts of Childhood That Haunt Your Clients’ Love and Work, had already been practicing for about 15 years when she started to understand just how much those dynamics might have shaped her clients. A deeply depressed man who began seeing her said that he’d already tried other therapists who hadn’t helped. So she asked him to come in with someone who knew him well. “I assumed he would bring his wife,” she told me. He brought his brother.

Lewis realized that without asking her clients specifically about their siblings, she might have been missing a key to their problems. She believes now that many people feeling stuck in a friendship or romance are to some degree stuck in patterns from early siblinghood—what she calls a “laboratory for learning everything you need to know in your adult relationships.” Runt told me she sees this in her work, too—perhaps one sibling felt they had to take care of the other, for instance, and then in adulthood they’re always trying to solve others’ problems.

[Read: What it’s like to visit an existential therapist]

Discussing siblings in individual therapy can be illuminating, but coming in together might be the only way to mend a rift—whether between pairs or a whole group. (Lewis has worked with a family of 10 siblings.) Sibling therapists told me that many clients go decades before seeking help; busy with their new family, perhaps they ignore pain stemming from the family they grew up with. Then their kids get a little older, and as they get closer to the end of their life, they start to reflect. “I have had siblings who have not talked to each other for five, 10 years,” Lewis told me. “Now they have more energy to be angry.” Other times, some event will force them together, such as a parent getting sick and needing care, or dying and leaving logistics for the siblings to tackle. Perhaps the siblings want their own kids to have a cousin relationship, or one child is getting married and invites an aunt or uncle to the wedding. Sometimes a person just realizes they don’t want to die before reconciling with their sibling.

People often reach this conclusion in midlife. Lewis works largely with clients in their 40s to 60s, though she does see a set of sisters in their 90s. She referred to this as the “hourglass pattern” of a sibling relationship: a lot of contact in the beginning of life, then a period of distance—then a reunification before it’s too late.

The Beaudoin brothers, who are in their 30s, saw going to therapy together as a final effort to rebuild their relationship. “We really only had one shot,” Dan said. Lewis, they told me, essentially served the role of a parent wrangling her squabbling little boys. She wasn’t afraid to jump into their arguments. She would cut off their tangents or call them out on deflecting blame, and then she’d pull them back to important questions about, say, their communication patterns. (Sometimes sessions do get heated, Lewis told me, but other times siblings are so distanced that they’re too polite. “They talk from their head,” she said, in which case she tries to “get that heat out.”) Through that process, Cam and Dan finally started to see the problems with their own interactions—the same issues that had plagued them for so many years. Dan, a talker, would exasperate Cam when he went on for too long; Cam would shut down, and his silence upset Dan. With Lewis, the brothers developed hand signals and code words to quickly show when a conversation is feeling too emotionally intense—and also the language to say “I don’t want to talk about that,” Cam told me.

[Read: The great cousin decline]

Sibling therapy isn’t all about hashing out current conflicts, though; it also involves going back in time. Because siblings typically grow up in the same home, they tend to assume they had similar childhoods. But often, that’s not true. “You may have had completely different experiences based on how skilled your parents were at parenting at that point in time, what stressors were involved, what money looked like, and also your birth order,” Runt told me. (Studies suggest there’s no consistent effect of birth order, but that doesn’t mean that it doesn’t influence dynamics—just that it likely does so in different ways for different families.) Sibling therapists ask questions to see where narratives match and diverge, what Runt calls “comparing notes.” What was your sister’s role? Who was your mom’s favorite? What was it like at the dinner table? That context can explain a lot about a sibling’s behavior.

The goal of this work isn’t necessarily to become best friends. Sometimes it’s to survive family gatherings or to come together to care for a sick parent; other times, it’s about letting go of pain, even if you don’t keep in touch after you leave the therapy room. You could think of sibling therapy, in those cases, as harm reduction. Not all siblings can or should be in each other’s lives. But the ones who manage it get something unique from one another, however fraught their time together is: Even if a sibling didn’t have the same childhood as you, they’re probably likelier than anyone else in the world to understand where you came from. They might be the only one who can tell you, with firsthand knowledge: “Your experience is real,” Runt said. Without that, “we’re the only one who knows that and can validate that for ourselves. And that’s a lonely place to be, right?”

A lot of Americans are in a lonely place, and most of the proposed solutions focus on friendship: cultivating relationships with the people we’ve chosen to hang out with and build our adult lives with, rather than the ones we got stuck with at birth and might see only at Thanksgiving. But Robert Waldinger, a psychiatry professor at Harvard Medical School and the lead author of the study finding that sibling closeness predicted depression at age 50, told me that many siblings know they can count on one another when needed, even if they’re not emotionally close—giving one another what he called “instrumental support.” In a more recent study, he asked middle-aged participants: “Who could you call in the middle of the night if you were sick or scared?” They could list as many names as they wanted—and some people didn’t have a single one to write down. But many, he said, listed a sibling.

The siblings I spoke with said that their relationships hadn’t been completely transformed by therapy so much as subtly shifted, enough to delicately start again. Cam and Dan are working on keeping expectations for each other realistic: They don’t need to talk all the time, or agree on all the things that once tore them apart. But they’re moving ahead—not just for themselves, but to show their kids what a healthy sibling relationship can look like. “We have to build that,” Dan said. “We have to be the ones to model it.”

​​When you buy a book using a link on this page, we receive a commission. Thank you for supporting The Atlantic.

The 'MacLeod Course' is named after Mr Trump's mother, who was born on the Isle of Lewis.