We all know sibling rivalry is common among kids. But it can last decades after childhood has ended.

Scroll through online message boards and forums, and you’ll find a slew of stories. Grown-up brothers and sisters bicker. Push each other’s buttons. Steal money from one another. Play cruel pranks. Even physically fight. Some just squabble. Others cross the line into sibling abuse.

These fights may come as a shock to parents. Clinical psychologist and professor Laurie Kramer, PhD, once asked her students at Northeastern University to write down the worst thing that had happened between them and their siblings that their parents didn’t know about.

“Everybody had something,” Kramer says. “It was really eye opening.”

Many siblings outgrow their rivalries. They step back from it, perhaps after a particularly nasty fight. But not all do that.

While there’s no simple solution, there are strategies that help dial down the conflict.

It usually comes down to how children feel they’re being treated by their parents.

Being treated differently by a parent, whether it’s real or perceived, is one of the most consistent predictors of sibling rivalry and competition – and not just as kids. Megan Gilligan, PhD, an Iowa State University associate professor of human development and family studies, has seen it across the board. “We’ve found it when folks are in their 50s and 60s, and even after parental death.”

As grown-ups, tensions can mount over who is perceived as more happy or successful. The conflicts may be verbal. Think: sniping at each other with disdain or sarcasm.

If it goes beyond friendly bickering, this can take a toll on a person’s mental and emotional well-being. This is especially true if one sibling is more ready to get past it than the other. Some even cut all ties because they just can’t get along. And it probably didn’t start out of the blue.

Even as kids, sibling relationships can be complicated and intense. Brothers and sisters don’t choose each other. It’s inevitable that at some point they’ll clash.

“It’s hard living with people,” says clinical psychologist Eileen Kennedy-Moore, PhD, author of Kid Confidence: Help Your Child Make Friends, Build Resilience, and Develop Real Self-Esteem. “They take your toys. They don’t do what you want.”

She says it’s human nature to compare ourselves to whomever is around. And nobody is closer than a brother or sister. Gilligan agrees. “They’re one of the first people that we compare ourselves to.”

Children can feel stuck in certain roles within a family. Think of a family with one rowdy child and one quiet one. The rambunctious one might think that their parents love the calmer one more. And the calmer one may feel shoved into the role of being “the good one.”

Unless kids get the chance to step out of those rigid roles, rivalries or resentments can fester over time. And that can lead to fights, jealousy, or constant one-upmanship.

A lot of siblings go through this. “Often people will think there’s something wrong with their family, something pathological,” Gilligan says. “But it happens in most families.”

Even beyond middle age, siblings still remember the way they felt as kids. This affects their relationships with each other and their psychological well-being.

“It sticks with us,” Gilligan says.

This is especially true with severe or unhealthy conflict. But it can happen with milder cases, too. Says Kennedy-Moore, “It really depends on the meaning that people attach to the past events.”

Wellesley, MA, therapist Omar Ruiz puts it this way: “Kids are impulsive. Adults are intentional.” You have choices and skills now that you didn’t have back then.

You may have known your brother or sister your whole life. This makes the sibling relationship different from the ones you have with friends, partners, or even your parents.

This is why we often fall back to our family patterns and behaviors when we’re around our siblings – at holiday dinners, for example. “It is easy to get caught up in these types of situations,” Ruiz says. “There are more people that may add pressure for you to respond.”

Plus, we tend to go back to shared experiences that we had growing up. “Your behaviors and mannerisms are going to draw from that history,” Gilligan says. So it will take work to take your relationship off autopilot.

Having similar values is one of the best predictors of our personal relationships, including with siblings.

“We tend to maintain relationships with individuals who share our values and beliefs. When we have different values and beliefs, we’re more likely to terminate those relationships,” Gilligan says.

If someone with very different values isn’t a relative, we might choose to cut ties. But it often feels different with siblings. “There’s always going to be some degree of family obligation that’s going to pull you back,” Kramer says. 

Sometimes, a little space can help. Some siblings say that they only started to see an improvement in their relationship when one of them moved away. This can be a healthy way to redefine yourself apart from your sibling. “You need your own identity,” Kramer says.

Sometimes, the best way to move forward isn’t by calling a moving van. It’s by agreeing to disagree, at least temporarily. You may not be able to forge a deep friendship with your sibling, but you can at least interact more peacefully.

Challenge yourself to better understand your brother or sister’s perspective, goals, needs, and preferences. This takes skills like compassion and listening.

Their experience may have been different from yours. Even trivial things can spark a relationship rift that lasts for years. You and your sibling may not even remember what caused the break.

“It just gets translated into a bad feeling about this person,” Kramer says. “They hold on to the negative feeling, not the fact.”

Many people don’t have someone they feel comfortable talking to about it. So they form their opinions about their childhoods in a vacuum, rather than seeing the whole picture.

“As people grow up, they develop more and more complicated narratives about their relationships,” Kramer says.

Those explanations aren’t always accurate. When experts compared parents’ reports to those of their adult children, for example, they often did not line up.

Gilligan points to researchon this. “When we ask mothers about who they are emotionally close to — who they would prefer as a caregiver — the children know that the mothers have these preferences, but they are wrong in terms of who it is.”

You’ve probably changed since childhood. So allow that your sibling may not be the same as they once were.

“Be open and curious to discovering who your sibling is,” Kennedy-Moore says.

If you find yourself falling into old patterns, try starting afresh. “The sibling relationship really can be wonderful if we let it,” Kennedy-Moore says. “But we have to build it up the same way we would a friendship.”

It’s crucial to have empathy and look forward. “Try to give people grace,” Kennedy-Moore says. “We make mistakes. We are insensitive. We lash out. The real question is: What happens now?”

Communication is key. Clearly state your own needs to your brother or sister. Let them know what you need from them, what is no longer true about yourself, and what you care about.

“They’re not going to know automatically,” Kennedy-Moore says.

She recommends using the phrase, “I need you to blank because blank.” For example, “I need you to not leap in with advice because it makes me feel like you don’t trust my judgment.” Or “I need you to not ask me questions about this topic because it stresses me out.”

As kids, we don’t have the self-control to stay calm in times of competition, Ruiz says. But as adults, we can.

“You and your sibling are no longer children, neither in age nor in brain development,” Ruiz says. “You are in the position to be more intentional about the choices you make.” You can choose to stay in the present rather than dwelling on old wounds.

Don’t assume and don’t fix. You probably don’t know exactly what your sibling thinks or feels – or what they need. “Many adults feel like they can solve a problem by ‘fixing’ the person,” Ruiz says. “Family members become resentful of this.”

Instead, try to be empathetic. This means putting yourself in your sibling’s shoes. Think about why they might have acted a certain way.

If they were abused, for example, trauma is often a trigger. “This does not excuse their behavior, but rather provides necessary context to why they act the way they do,” Ruiz says. If there has been trauma, he adds, sometimes it’s best to create clear and healthy boundaries rather than force a reconciliation.

Don’t overlook your own part. “It’s actually good to think about your role in it because that gives you more control,” says Kennedy-Moore, “Whatever the dance is, you can do something different on your part, and evoke something different on their part.”

Don’t count on things magically working out. “These are decades of patterns of behavior,” Gilligan says. “It’s not just going to come back together, even during major life events. If someone really wants to repair a sibling relationship, it’s something that they have to be really intentional and thoughtful about.”

If you are serious about mending a strained sibling relationship as an adult and what you’ve tried isn’t working, it can help to talk with a therapist.

Consider what you both could gain if you can reach some degree of reconciliation. Less stress? A closer relationship?

“Both the beauty and the difficulty of the sibling relationship is that they’ve known us forever,” Kennedy-Moore says. “It’s very easy to slide into the, ‘This is exactly like what you did when you were 11!’ kind of scenarios. On the other hand, they’ve seen you at your worst, and they still love you. That’s wonderful.”

Making room for the good parts of the relationship – or at least dialing down the toxicity – could be the shift you’ve both been waiting for.