Why do siblings fight so much?
Because they are competing for genuinely limited resources, in a relationship they cannot exit, with someone they must share an environment with indefinitely — a combination that would produce conflict between any two people.
The structural reasons:
Competition for parental attention, which is finite and highly valued. This is the underlying driver of a great deal of what looks like conflict over objects.
No exit. Friends who fight can avoid each other. Siblings cannot, so conflicts recur rather than resolve.
Enforced proximity and shared possessions, space and routines.
Comparison. Siblings are constantly measured against each other, by parents, teachers and themselves, and comparison is a reliable source of resentment.
Safety. Home is where children can be at their worst. Conflict with a sibling carries little social cost, so behaviour that would be suppressed elsewhere is expressed there — the same reason children behave worse for their parents than for anyone else.
A low-stakes practice arena. Siblings are where children learn to argue, negotiate, share, apologise and repair. Some conflict is developmentally useful, not merely tolerable.
What the research indicates about parental response:
Trying to adjudicate every dispute frequently makes things worse. It rewards escalation — whoever is louder or reaches the parent first gains an advantage, so the incentive is to escalate and involve the parent.
Perceived unfairness matters more than actual fairness. The evidence on differential treatment is fairly consistent: children's perception of being treated less favourably predicts worse sibling relationships and worse outcomes, and children detect differential treatment accurately.
Fairness is not sameness. Treating children identically regardless of age or need is not experienced as fair either. Explaining the reasoning matters more than equalising the outcome.
Labelling roles — the clever one, the difficult one — entrenches rivalry and is difficult to undo.
What helps: coaching rather than judging, so children learn to resolve conflicts themselves; separate one-to-one time with each child, which reduces competition at its source; not requiring insincere apologies; intervening firmly where there is a genuine power imbalance, since sibling bullying is real and is under-recognised; and accepting that conflict frequency is a poor predictor of the adult relationship.