Why Did They Cheat? Five Explanations From Science

There are many reasons people cheat on their partners, from low self-esteem to high social media use. Or balls. Sometimes it might be balls.


Dr. Katie Spalding

Katie has a PhD in maths, specializing in the intersection of dynamical systems and number theory.

Freelance Writer

A woman looks suspiciously at her partner, who is on his phone.
My god..... they're right.... his balls are huge .... Image credit: Prostock-studio/

It's not a nice thing to think about, but the chance that you’ve been cheated on in your life is more or less the same as flipping a coin. And for everyone who discovers an infidelity from their partner – or who is perhaps shocked to discover themselves less tied to monogamy than they assumed – one question is bound to end up being asked: why? Is it me? Is it them? What happened? 

Well, of course science has looked into this – and it turns out there are quite a few psychological reasons behind the act of cheating on somebody. Some come from nature; some from nurture – and some may be a bit of a wild card. Let's have a look at just five of them now.


Cheaters may be liars – and not just to their partners

We may not all cheat on our partners, but there are plenty of things we do every day that we know are wrong. We eat meat, despite knowing how cruel animal agriculture is. We drive distances we could easily walk even though the world is already teetering on the edge of total climate collapse. And we manage to do this – mostly without experiencing excessive guilt or identity crises – thanks to a psychological trick called cognitive dissonance.

Infidelity is the same. “Cheaters might minimize the significance of their infidelity as a way to cope with knowing they did something wrong,” explained Benjamin Le, an associate professor of psychology at Haverford College. “[They] feel bad about their indiscretions, but try to feel better by reframing their past infidelities as uncharacteristic or out-of-the-ordinary behavior.”

They’re not good at confrontation

“People cheat often out of fear of facing conflict,” clinical psychologist Joshua Klapow told Bustle. “They know there are problems in the relationship."

"In some cases, the person feels there is nothing left. They have given up, but they don’t want to put an end to the relationship often for logistical reasons – money, kids, lifestyle.”


As ways to alert your partner to problems in the relationship go, it’s not exactly the healthiest tactic – but it’s hard to deny its effectiveness. And while fewer than one in six couples remain together after an admission of infidelity, breaking up is sometimes the last thing a cheater wants to do. Strange though it may sound, Klapow explained, sometimes “people cheat to keep the relationship together … they love things about their partner, but there are other aspects that are not there. 

“The person doesn’t want to leave but doesn’t know how to pull these other qualities out,” he said.

They’re scared

Some people – especially people with a history of trauma or abuse – have a real hard time opening up. And if they feel that the relationship is going too fast, or getting too intimate, that might trigger what’s called an avoidant attachment response – in other words, they cheat as a form of escape.

People with avoidant attachment styles “rarely feel more connection with an alternate lover than they do with their long-term partner,” explained Hal Shorey, a clinical psychologist and professor of clinical psychology at Widener University, in an article for Psychology Today


“They seem to view the sexual connection as a welcome distraction or form of exciting entertainment,” he wrote. “Often, they have no intention of leaving their relationship.”

And sometimes, the problem is the exact opposite: someone who feels their partner is not emotionally available enough may have an anxious attachment response – they become convinced that the relationship is doomed to fail, and so take out what Shorey calls “an insurance policy” relationship.

“In other words, they may sense that if the relationship came apart, they would be so distraught that they would not be able to cope. They may try to line up another romantic partner so that they have someone to go to if their primary relationship fails,” he said.

They’re a psychopath

There are a ton of studies out there showing that people with Dark Triad personality types – people who score highly in narcissism, psychopathy, and Machiavellianism – are more likely to be unfaithful.


But why? It actually depends on which area of the triad a cheater scores highest on. For example, one study, published in the journal PLOS ONE in 2020, found that narcissistic individuals tend to create more superficial and less satisfying relationships, based on their own need for praise rather than any desire for warmth or romantic connection. 

“Narcissism is associated with a game-playing love style, low commitment, and infidelity,” the authors write. “Prior research has also shown that narcissists in long-term romantic relationships demonstrate low levels of commitment, are susceptible to infidelity, and have a greater number of divorces than non-narcissists.”

But while narcissists may cheat due to a lack of commitment, Machiavellians and especially psychopaths can cheat for more spiteful reasons. 

“Dark Triad traits are consistent predictors of revenge and its planning, especially psychopathy and Machiavellianism,” explains a 2021 paper published in the International Journal of Environmental Research and Public Health. 


“Revenge is associated both with cognitive and emotional components, and this is especially relevant in the case of infidelities,” the authors write, warning that “more efforts are made to harm than to protect oneself against possible retaliation, suggesting that the dark trait of malevolence, which entails seeking to harm to others even if one suffers harm, may be involved in the process.”

They spend too much time on Twitter – or masturbating

It would be pretty impossible to investigate why people cheat on each other in a fully randomized experiment, so most of the evidence for predictors comes from observational studies. The problem with that is (say it with us) correlation is not causation – and observational studies are bound to throw up some weird results.

So while we’re not saying these are the reasons behind somebody cheating, the following have all been found to be associated with a higher risk of it happening:

1. Twitter use: A 2014 study found that higher social media usage, and Twitter in particular, was linked to negative relationship outcomes, including infidelity and even divorce.


2. Too much, ahem, “solitary desire”: When a 2021 study used machine learning to try to predict the biggest risk factors for cheating, one result pretty consistently topped the list. Higher levels of solitary desire, or as it’s known outside of scientific circles, wanking, were associated with an increased incidence of infidelity – as were higher levels of anal sex and sex toy use. The researchers, led by sex and relationships researcher Laura Vowels, explained this relationship in terms of a potential confounding variable: sexual permissiveness.

3. Balls too big: Yes, the secret reason your partner cheated on you may be due to the size of your testes. A 2014 study found that in primates – of which humans are an example – “we can determine the degree of fidelity in the female by looking at the size of the male's testicles,” explained University of Oslo zoologist Petter Bøckman. “The less faithful the female, the larger the male's testicles.”

“Bonobos in particular have huge testicles. They mate with everybody,” he said. “In gorilla troops there is only one male. Even though the gorilla has a small harem, he has no need for large testicles – his balls are tiny.”

Of course, while there are many reasons somebody may cheat in a relationship, the truth is often far more complex. And that means that recovering from infidelity – or preventing it in the first place – can be just as tricky to figure out.


“Overall, I would say that there isn’t one specific thing that would predict infidelity,” Vowels told PsyPost. “However, relationship related variables were more predictive of infidelity compared to individual variables like personality.” 

“Therefore, preventing infidelity might be more successful by maintaining a good and healthy relationship rather than thinking about specific characteristics of the person,” she said.


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