While few adult siblings have severed their ties completely, approximately one-third of them describe their relationship as rivalrous or distant. They don’t get along with their sibling or have little in common, spend limited time together, and use words like ‘competitive,’ ‘humiliating,’ and ‘hurtful’ to depict their childhoods. The speed with which old conflicts reduce these adults to children again prevents them from seeing one another in a new or different light. They push each other’s buttons without knowing why or how and recast themselves in childhood roles that never worked in the first place.

Interestingly, the most rivalrous of sibling pairs are brothers, the author says, with identical male twins being the most competitive.

Rivalry is also one of the themes of Jane Isay‘s 2010 book Mom Still Likes You Best: Overcoming the Past and Reconnecting With Your Siblings. It all begins in early childhood situations, she says. However, “Even when we’re in our seventh and eighth decades, brothers and sisters can still push our buttons.”

Elaboration on the origins of both good and bad experiences (Today.com):

When young siblings are unsupervised, the time they spend together gives them the opportunity to experience every imaginable emotion and to express their feelings unfettered by the adults in their lives. Might makes right, older kids hold the power, younger ones snitch and bite; they steal from each other, tease each other, make each other cry, grab each other’s toys, pinch each other’s arms, and sneak each other’s food…By the same token, children give each other a degree of support and comfort they cannot find elsewhere.

Significantly, this happens, Isay explains, before our brains really understand things and at a time of life easily forgotten many years later. “Memory flashes beyond our control emerge from a long-ago time when we were trying to make sense of our world with the limited understanding of children. They are pure emotion, unfettered by reason.”