Even the happiest couples encounter conflict. But what they fight about reveals a lot about what’s missing in the relationship.

As a psychologist who studies couples, I’ve found that there are a few similar topics that come up again and again. And the first step to resolving the conflicts is to know what those topics are.

According to a YouGov poll of 1,000 American adults, and based on my research, here are the most common reasons couples fight — and the psychology behind each one.

A sour tone or attitude — a slightly raised voice, a sarcastic comment, an eye-roll mid-conversation — is by far the most common reason couples fight. To the person exhibiting it, it might not seem like a big deal. But to the partner on the receiving end, it hits a direct nerve because it signals contempt.

In marital research, contempt is one of the most reliable predictors of divorce. Unlike overt criticism or stonewalling (shutting down emotionally), contempt disguises itself with non-verbal gestures and body language.