Adult friendships are already operating on borrowed time. Between jobs, kids, relationships, and the general exhaustion of being a functioning person, maintaining a friendship takes major effort. What’s harder to spot — and harder to admit — is when a friendship isn’t just difficult to maintain, but fundamentally imbalanced.

According to Psychology Today, the single habit most likely to kill an adult friendship is nonreciprocity: the slow, compounding dynamic where one person is always giving and the other is always taking.

Every friendship goes through lopsided seasons. Someone loses a job, goes through a breakup, has a hard year — and the other person picks up the slack. That’s what friends do. The issue is when one person is always the one picking up the slack, and the other is always the one dropping it.

When Every Interaction Tilts One Way

The first place it usually surfaces is in how someone actually shows up for you. The friend who never reaches out is easy to identify. Trickier is the friend who does reach out — but only when they need something. They text when they’ve had a terrible day and need an hour of your time. Two weeks later, when you’re going through something, they send a few sympathetic words before steering the conversation back to themselves. The interaction exists. It just never goes in your direction.

The science gives this some context. A 2009 study using the National Longitudinal Study of Adolescent Health found that reciprocated friendships ranked among the strongest indicators of social support, outranking simply having more friends or talking more frequently. It’s not the volume of contact that matters, but whether the exchange actually benefits both people.

When it doesn’t, you can feel it before you can name it. The conversations start feeling like obligation. You get off the phone more exhausted than when you picked it up, and a low-grade resentment sets in. Since the friendship looks fine from the outside, you spend more time questioning yourself than questioning the dynamic.

When Their Boundaries Are the Only Ones That Count

Boundaries have become such a fixture of the wellness conversation that using the word has started to signal emotional sophistication all on its own. But a weaponized boundary can do just as much damage to a friendship, especially when they only flow in one direction.

The scenario usually looks like this: they need space when they’re overwhelmed, and you give it. When you go quiet for the same reason, they’re offended. They bow out of plans whenever they’re not feeling up to it, but when they want to see you, canceling isn’t really an option. One person’s limits are treated as law. The other person’s are treated as negotiable.

A 2008 study from the Journal of Emotional Abuse describes this as boundary dissolution — the breakdown of appropriate limits between individuals that increases the risk of emotional harm. Boundaries are meant to protect both people. When they only serve one person’s experience of the friendship, they’ve become something else: unspoken rules that establish a clear hierarchy about whose needs actually matter.

If you’ve ever left a friendship feeling inexplicably worse about yourself, that’s your answer.