From Our Archives, originally published January 12, 2017.

Siblings are our longest-lived and often among the most complex relationships. No matter how old we are, the template of our early family stays with us throughout our lifetime. Naturally, we mature, develop and gain insight into ourselves and wisdom about others. As a result, many relationships become smoother and more peaceful. One relationship remaining troublesome can be between siblings.

Conflict between siblings is so ubiquitous that I would guess that on a word association test most people would say “rivalry” when prompted by the word “sibling.” But what’s more surprising is how much of the conflict persists as we age. Below are five common issues that persist often well into midlife (and beyond):

Rivalry

Rivalry is by far the most common, persistent, and resistant to change of the sibling issues. Sometimes it is the result of an accident of birth order (e.g., two siblings of the same sex, close in age), and many times it is exacerbated by real family dynamics  (e.g., Mom really did like you best). Most often it is a very complex combination of many factors, including, but not limited to those above.

Unfortunately, parents can favor one child over another without being aware of it, and though the difference may be subtle, the effects may be dramatic.

Sometimes, the rivalry can wax and wane over the course of adulthood, as we see that life doesn’t always favor one person over another and your rival may come in for her share of hard knocks. But that may not be the case, and furthermore, the competitive spirit can be lodged so deep that we are not appeased and continue to feel threatened no matter what the circumstances.

These feelings not only disrupt our relationships with our adult siblings but also have the power to be transferred onto others in our life. If you have had a history with a sibling laced with unresolved feelings of competitiveness and her “evil twin,” envy, chances are these issues pop up in your other relationships as well.

Failure to Separate

On the other hand, some siblings stay close as they grow older, which is fine until it presents a problem for our independent relationships. A typical scenario involves one wanting to move on (often with a romantic partner), which upsets a long held balance between two very close siblings. This can set up seething rivalry and resentment between the new spouse and the “left out” sibling that is never fully resolved, even after the second sibling is married.