In 2009, Carrie Underwood sang about assaulting her boyfriend's truck with a Louisville slugger in an effort to prevent him from cheating on her, or whoever he dated after her, again. In both Carrie's world and the real world, "once a cheater, always a cheater" is accepted as an unquestionable fact.

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But then, in 2017, that cliché about repeating infidelity was finally put to an academic test when the Archives of Sexual Behavior published the very first legitimate study on serial cheating.

"That study was the first that gave us any scientific insight into whether there's any truth to the idea of 'once a cheater, always a cheater,'" says Dr. Justin Lehmiller, a research fellow at the Kinsey Institute and author of . The study, which Lehmiller wrote about in 2017, surveyed 484 adults who admitted to cheating in previous relationships and found at least a little bit of truth behind the phrase. Researchers found that people who cheated in one relationship were about three and a half times more likely to cheat again. Which doesn't prove the cliché to be an absolute truth, because as Lehmiller points out, plenty of those surveyed cheated once and never again.

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"It's one of those things where there's a kernel of truth to it," Lehmiller says. "There's some data, scientifically, to back it up, but it's definitely not true in all cases."

There's obviously no one reason why people cheat. But Lehmiller says a study from one of his colleagues at the Kinsey Institute might have found what some call the infidelity gene. "Some people are sensation seekers, and they have this heightened need for thrilling and risky sexual encounters," Lehmiller explains, and researchers found that heightened need for "risky sexual encounters" is tied to a deficiency in dopamine receptors—or the part of the brain that's involved in feeling pleasure. In other words, thrill seekers need bigger thrills (in this example, sneaking around and cheating) to feel the same amount of pleasure.

If you're reading this and thinking of preemptively slashing your current partner's tires because you know they cheated in the past, hold on a sec. Rachel Sussman, a relationship therapist in New York City, says she sees plenty of people in her practice who cheated once, and say they'll never do it again—whether they got caught or not.

"I've seen people who've cheated and they see how much pain it's caused the person who they were with, and they'll say to me, 'I'm happy I got out of that relationship, but I feel absolutely terrible over how I did it,'" Sussman says.

Essentially, Sussman says "once a cheater, always a cheater" is just another way of saying people are incapable of feeling remorse and of changing. And Lehmiller agrees, emphasizing that while the study on serial cheating seems scary and ominous, it's by no means an endorsement of the cheating cliché. Once a cheater doest not make an always cheater. Now put the baseball bat down.

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Hannah Smothers Hannah writes about health, sex, and relationships for Cosmopolitan, and you can follow her on Twitter and Instagram

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