Everyone has regrets. Of course, what it is that we regret varies from person to person, but if you look at the general areas in which people express regrets, sex tends to top the list.

For example, in a 2012 national US phone survey in which American adults were asked about their most memorable regrets, the most common things people said they were sorry for doing—or, in some cases, not doing—revolved around sex, love, and romance.

A set of three studies exploring sexual regrets in more detail found a reliable gender difference when it came to how people felt about casual sex specifically. Published in the Archives of Sexual Behavior, this research revealed that women are more likely than men to regret previous experiences with casual sex. By contrast, men were more likely than women to regret opportunities for casual sex that they passed up. In other words, women were more inclined to regret their sexual actions, whereas men were more inclined to regret their sexual inactions.

So why are women more likely than men to have regrets about one-night stands and other forms of casual sex? A forthcoming study published in the journal Personality and Individual Differences explored the psychology behind this gender difference, and the results suggest that there are several contributing factors.

In this study, 547 Norwegian and 216 American adults completed a survey that focused on how much regret they felt about their most recent casual sex experience. As part of the survey, participants reported on various things that might contribute to feelings of sexual regret, such as feeling disgusted by the encounter or having a partner who was sexually incompetent.

Consistent with previous studies, both Norwegian and American women (41-50 percent) were more likely to regret the most recent time they had casual sex than did men from these countries (26-35 percent).

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Compared to men—and across both nations—women rated their most recent casual sex experience as less physically gratifying and more disgusting. They felt more pressured, thought their partners were less competent, and were more worried about the potential implications of it for their social reputation and sexual health. Women were also less likely to initiate the encounter.

All of these factors tended to predict feelings of sexual regret; however, some were stronger predictors than others. Specifically, feeling disgusted (both physically and morally) was the single biggest predictor of experiencing regret, followed by low gratification and sexual incompetence, health and reputational concerns, and not taking the initiative. Feeling pressured didn’t predict regret above and beyond these other factors, but that’s probably because it was statistically redundant with some of the other variables that were tested. This makes sense when you consider that feeling pressured was strongly related to feeling disgusted and worried, especially among women.

Generally speaking, the same factors predicted sexual regrets for women and men. In other words, both women and men regretted casual sex when they felt disgusted by it, when it wasn’t pleasurable, and when they experienced worries or concerns about it. Because women tend to experience more disgust, less pleasure, and more concerns in the first place, this helps to explain why women’s baseline level of casual sex regret is higher.

There was one predictor of regret that differed between men and women, though, which was taking the initiative to have casual sex. When women initiated casual sex, they were less likely to regret it. However, taking the initiative was unrelated to whether men had regrets.

This initiative finding is interesting and worthy of further study. Could it be that when women take the initiative, it means that they find their partners to be more desirable? Alternatively, perhaps this finding simply reflects the standard sexual script that prioritizes male over female pleasure, which makes it harder for women to say no to casual sex.

It’s important to note that this research didn’t take into account all possible reasons that people might regret casual sex. For example, self-esteem as well as alcohol and drug use are probably relevant, too. It’s also possible that the factors that lead to sexual regret differ at different stages of life.

Limitations aside, this research offers an important glimpse into the psychology behind gender differences in regrets over casual sex. Though more research is certainly needed, the hope is that we will develop a more complete understanding of the origin of this gender difference over time so that we can work to turn casual sex into an experience that everyone—especially women—looks back on more favorably.

Justin Lehmiller is the director of the social psychology program at Ball State University, a research fellow at The Kinsey Institute, and author of the blog Sex and Psychology. Follow him on Twitter @JustinLehmiller.