Even if no-strings-attached sex seems great at the moment, post-sex regret might creep up with the sunrise. And it seems to occur more for women than men, a study from Norway suggests. 

Researchers asked 263 people ages 19 to 37 how much they regretted either engaging in or passing up a recent casual sex experience. About 35 percent of women surveyed expressed regret, compared to just 20 percent of men. Plus, only 30 percent of women said they were happy with their most recent one-night stand, while around 50 percent of men said the same. (These are the new rules of one-night stands.)

So it’s not really a surprise that women were more likely to be pleased with passing on no-strings-attached sex: 80 percent said they were glad they declined a recent chance of casual sex. That’s nearly double the amount of men who said the same. (In fact, 30 percent of men regretted not getting frisky when they were given the chance.)

Women did worry more about pregnancy, sexually transmitted infections, and loss of reputation associated with casual sex, but those factors don’t account for the sex differences when it came to post-sex regret. Even the difference in sexual satisfaction didn’t seem to explain the disparity.

Instead, researchers suggested that it comes down to fundamental differences that tie into evolutionary psychology. Basically, women may be more wired to see sex as a way to have children with a supportive partner. A short-term rendezvous wouldn’t provide that for them. But for men, the results of short-term sex wouldn’t be so problematic—so they look for casual opportunities more than women do.