Men and women see cheating a little differently, study says. That leaves room for some real hurt.

Cheating on a partner is startlingly common in the United States. About 21% of men and 19% of women surveyed have admitted to infidelity, according to a 2015 YouGov online survey. Other research has found similar numbers: A 2010 General Social Survey from the National Opinion Research Center, for example, found that about 20-25% of men self-reported infidelity while 10-15% of women did.

Now, a study from the Norwegian University of Science and Technology is trying to understand the potential fallout of that infidelity. Researchers asked 92 heterosexual couples at the university how they’d feel in four different, hypothetical cheating scenarios.

All of the scenarios start out the same way: One person in the relationship goes to a party without their significant other and meets someone that they “danced intimately and flirted [with]” throughout the night. In two of the scenarios, the participant was the cheater, either having sex with the party-goer or simply partaking in the “emotional infidelity” of dancing intimately and flirting. In the other scenarios, the participant is the one being cheated on in these two ways (emotional or sexual infidelity). All of them were asked to rate their feelings about the four scenarios.

Participants were young — between 19 and 30 years old — and the average length of their relationships was one year and nine months.

Here’s what scientists saw.

Cheaters had a hard time believing they were forgiven.

Researchers noticed a phenomenon they call the “negative forgiveness bias.” In this case, it’s when the cheater underestimates how much their partner has forgiven them for their wrongdoing.

Both genders generally experienced this bias, the researchers found.

“Negative forgiveness bias was present for both emotional and sexual infidelity scenarios, and for male and female participants,” the study stated.

But results really started to differ depending on whether the cheating was emotional or sexual.

Men and women saw emotional cheating differently.

Compared to men, women tended to believe that their partners hadn’t forgiven them for their emotional infidelity (dancing intimately and flirting at the party). Men were also generally more likely to forgive their female partner’s emotional infidelity — but that could be because they didn’t see flirting and intimately dancing as cheating.

In other words, genders tended to define cheating differently, with many men believing that sex is required for an action to be explicit infidelity.

Because of that, men also were more likely to believe that their acts of emotional cheating would be forgiven. Ignoring the pain of infidelity in itself for a moment, it’s easy to see how this could be a tragic mistake — imagine the pain of your partner admitting to emotionally cheating, only to think they’re off the hook shortly thereafter.

“Men understand that emotional infidelity is a problem,” the study said. “They just do not have insight into how great a problem their partner finds it to be.”

Both genders reacted severely to sexual infidelity.

Men were much more threatened by the idea of female partners sexually cheating on them than emotionally cheating. However, both genders generally rated the damages of sexual infidelity on their relationship to be about the same.

One fallacy of the study, however, is that it’s only measuring hypothetical scenarios. The real, raw emotions of finding out about a partner’s cheating could yield very different results.

Either way, at least among its participants in Norway, there seems to be mismatched expectations about what cheating even is.

“Even though both men and women perceive both emotional and sexual infidelity as relationship threats, they have very different appreciations of the severity of especially emotional infidelity,” the study stated. “This may potentially be a source of misunderstanding, conflict and miscommunication in couples, and maybe a topic that couple counselors need to address.”