“Why can't you be like your sister?” Sibling comparison and how you see yourself

“Your sister’s been promoted again. She really is a good girl.”

Christmas lunch. Mum brings the roast to the table and mentions the news in passing. The daughter sitting opposite is thirty-eight, with her own job, her own children and her own achievements. And yet in that moment she is not thirty-eight. She is ten, sitting at the same table with her school report in her hands, listening to the same tone: “Why can’t you be a bit more like your sister?” She smiles, says “great, congratulations” and barely speaks for the rest of the meal. On the way home she tells her partner she is tired. She is not tired. She has been compared again.

Being compared with a sibling is one of those experiences almost all of us know and almost nobody talks about seriously. It sounds like a trifle — they were only words, our parents meant well, we are grown up now. But when people in therapy talk about how they see themselves, a brother or sister turns up in the story surprisingly often. In this post I will write about why being compared with a sibling cuts so deep, what research knows about parents treating their children differently, and how all of this lives on into adulthood.

Same family, different childhoods

One of the most surprising findings in developmental psychology is that children from the same family are often very little alike. Biological siblings share on average half of the genes that vary between people, grow up in the same house, with the same parents, at the same table. Even so, in an influential review in 1987 Robert Plomin and Denise Daniels showed that in personality they are often almost as different as two children from different families.

Their explanation was that an important part of the environment is non-shared: each child in the same family actually grows up in a slightly different family. The first child gets young, uncertain parents and a few years of their undivided attention. The second gets parents who are more relaxed and more tired, and an older brother who has already claimed some of the space. The third may arrive during a divorce, a move or an illness. Each gets a different relationship with their parents — and a different view of themselves.

This non-shared part of the environment is often exactly what children know most precisely: who gets more attention, who gets more patience, who is allowed what the other is not. Children are remarkably sharp observers of fairness.

Parental differential treatment: what we know

The research literature uses the term parental differential treatment for this — differences in warmth, attention, supervision, punishment and praise that children in the same family receive from their parents.

Mark Feinberg and Mavis Hetherington showed, in a study of families with two adolescents, that how a parent treats one child compared with the other is linked with how the children adjust — over and above how the parent treats each one individually. In other words: it matters not only whether Mum listens to me. It also matters whether she listens to my sister more.

It is important to say that some differences are not only unavoidable but right. A fifteen-year-old may stay out later than a ten-year-old. A child with a chronic illness needs more care. Two children with different temperaments need different responses. A good parent does not treat all children the same — they treat each one as that child needs. The problem starts elsewhere.

It is not the difference that hurts, but what it means

The key finding in this area came from Ann Kowal and Laurie Kramer. They asked children not only whether their parents treated them and their sibling differently, but also why they thought that was and whether it seemed fair. It turned out that most children were aware of the differences. But those who understood a difference as justified — “my brother is younger”, “my sister is ill” — did not show a worse relationship with their sibling. Problems were linked mainly with differences that seemed unfair or inexplicable to the children.

This is an important message for parents, and for adults looking back. The same difference can tell a child two very different things.

When nobody explains a difference, the child explains it to themselves. And children explain things mainly in relation to themselves: if my sister gets more, it is because I am less. In this way an outer difference turns into an inner belief that remains long after the circumstances have been forgotten.

Labels and roles: “the clever one” and “the lively one”

Comparison in a family rarely happens as a single remark. More often it happens as a label that sticks. “She’s the clever one, he’s the sporty one.” “She’s the responsible one, he’s our little rascal.” “She’s the pretty one, you’re the one with soul.” Labels are often born of love and of the wish for each child to have their own place. But when two children in the same family are split into opposite poles, each gets only half.

Researchers have noticed that siblings close in age often, consciously or not, choose different domains: if the brother is good at maths, the sister turns to music. This has been called de-identification — moving away from a sibling in a way that reduces competition. Sometimes this is a healthy solution. Sometimes, though, it means a child has given up something that would have brought them joy, simply because that place was already taken.

Labels often fold into larger family roles — the hero, the scapegoat, the invisible child. I wrote about this in more detail in Roles in the family: the hero, the scapegoat, the invisible child. Which was yours?, and you will also find a short description in the knowledge base under roles in the family. What matters for this post is something else: a role is not only something a child plays. It becomes part of what they believe about themselves.

Why comparison with a sibling cuts deeper

Who we compare ourselves with is not a matter of indifference. The psychologist Abraham Tesser described how another person’s success threatens us most when two conditions are met: the person is close to us, and they succeed in an area that matters to our own self-image. A stranger’s success in an unrelated profession leaves us cold. A friend’s success in an area where we, too, wanted to succeed hurts.

A sibling meets both conditions more than anyone else. They are close — in age, in origin, often in appearance. And they compete in the area that matters most to a child: for the love, attention and approval of the same two people. That is why being compared with your sister is not the same as being compared with a classmate. A classmate may be better at maths. A sister may be a better daughter.

From this comes a feeling people often find hard to name — not just envy or anger, but shame: the sense that something is fundamentally wrong with me. And the voice the child heard at the table gradually moves inwards. If your inner critic sounds like a parent comparing you, that is no coincidence.

Rivalry: competing for the same love

Sibling rivalry is part of almost every childhood and is not in itself a sign that something is wrong in the family. Children fight over toys, over the front seat in the car, over who gets the shower first. Through these quarrels they learn to negotiate, to give way, and that it is possible to fall out and still love each other.

Comparison sharpens rivalry. When a parent says “why can’t you be like your brother”, they put the siblings into a contest neither of them chose. The one compared downwards learns resentment. The one compared upwards often carries a quiet burden: having to be good all the time, not being allowed to disappoint, and often guilt towards the brother or sister who lives in their shadow. Comparison does not harm only one child. It harms the relationship between them.

How siblings connect with each other and with their parents — who sides with whom, who is whose ally — is a separate topic I wrote about in Siblings, alliances and coalitions: the invisible geometry of a family. Here I am more interested in what comparison does to how a person sees themselves.

How comparison lives on in adulthood

It would be nice if all this ended when the children left home. It does not. The American researchers Karl Pillemer, Jill Suitor and colleagues have for many years followed older mothers and their adult children. They found that most mothers could readily say which child they felt emotionally closest to, and that adult children often sense this. Perceived maternal differentiation was linked with more depressive symptoms in adult children — and not only among those who felt overlooked, but also among those who felt they were the favourite.

A study of young adults likewise found that “life still isn’t fair”: perceived unequal treatment by parents was linked with a poorer relationship between the adult siblings.

In adulthood comparison rarely sounds the way it did in childhood. It is no longer about school reports, but about jobs, salaries, partners, grandchildren, who phones more often and who turns up for Sunday lunch. It often returns most sharply at two points: when parents grow old and care for them has to be shared out, and when what they leave behind has to be divided. Then old stories about who was always “the responsible one” and who was “the one who was handed everything” often resurface with full force. If this theme is close to home, you may also want to read Adult children and parents: can the relationship still be repaired?

Comparison also lives on where there is no sibling. An adult who was always “the less successful one” may at work, too, constantly measure themselves against colleagues and experience every other person’s success as proof of their own inadequacy. The one who was “the successful one” may not know how to rest, because their worth has always been tied to achievement — this is also the subject of When you are worth only what you produce: self-image and productivity.

The conversation nobody started

Sometimes siblings only discover in adulthood that they experienced the same childhood very differently. Here is how such a conversation might sound. The conversation is composite and does not describe a real person.

“Did you know I envied you my whole childhood?”
“Me? Why?”
“Because you were always the clever one. Mum talked about you as if you were something special.”
“Ha. And I thought they loved you more. You were the one she laughed with.”
“Really?”
“Yeah. All she ever asked me about was my marks.”
A long silence. “So we both thought we were less.”

Conversations like this are rare because they are terribly hard to start. But when they happen, they often bring relief to both. It turns out that the contest they had been running all their lives was not a contest between them. It was a story each of them had read, in their own way, from the same parents.

In relational family therapy, in which I am training, a large part of the work is exactly this: separating what is mine from what I took on in the family, without giving up the relationship. We call this differentiation — the capacity to stay connected to your family while knowing who you are yourself.

Exercise: the label and you

This exercise takes about fifteen minutes. You will need paper and a pen.

1. Write down the label you were given in your family. One or two words: “responsible”, “difficult”, “the pretty one”, “less gifted”. Next to it, write the label your brother or sister was given.
2. Write down three moments from the past month when you acted in line with your label. What was it like? What would have happened if you had not?
3. Write down one thing you gave up because it “belonged” to your sibling. Singing, sport, drawing, loudness, tenderness.
4. Ask yourself: what would the label say today if it could see me from the outside? Would it still fit? Where would it not?
5. Choose one small action that does not fit the label. If you were always “the responsible one”, this week do not take something on. If you were “the less clever one”, take on something you have always left to someone else.

The exercise will not change the past. But it can help you notice that the label is not a fact about you. It was the way your family once arranged the space between its children.

Where this story does not hold

Here I want to protect this post from being misread.

Not every difference is favouritism. As I wrote above, parents have to treat children differently because children are different. If your brother was ill and got more attention, it does not necessarily mean Mum loved him more. It may mean she was frightened for him. An adult view of this can soften a great deal.

Birth order is not destiny. Persistent stories circulate about firstborns, middle children and the youngest. But a large study by Julia Rohrer and colleagues of more than twenty thousand people found no meaningful effects of birth order on personality traits. What happened in a particular family matters more than the place in which you were born.

Not everything is down to the sibling. Sometimes comparison with a sibling is only the most visible form of something broader — conditional acceptance the child would have experienced even as an only child. I wrote about where low self-confidence comes from in Where low self-confidence comes from: early experience and internal working models.

Parents are not the villains of this story. Most parents who compare do so out of helplessness, out of a wish to spur a child on, or because that is how they themselves were raised. That does not erase the pain they caused. But understanding where it came from often makes room for a different relationship — with them and with your sibling. If you are a parent yourself, a good first step is simple: explain the differences between your children and stop using one as the yardstick for the other. There is more on how teenagers experience comparison in Self-image in the teenage years: what parents can do.

What to remember

• Children from the same family actually grow up in slightly different families — with a different relationship with their parents.
• Parents treating children differently is not harmful in itself; what harms is mainly treatment that seems unfair and unexplained to the child.
• Comparison with a sibling cuts deeper than other comparisons because it is a contest for the same love.
• Childhood labels often turn into beliefs about yourself and live on at work, in partnerships and in the relationship with your parents.
• A label is not a fact about you — it was the way your family once divided up the space.