It's rooted in insecurity and an innate, albeit narcissistic, need to know we take the cake – that, as far as lovers go, we're the best our bae has ever had. (Newsflash: most of us probably aren't, and that's actually okay. But more on that later.)
Interestingly, a survey by Elite Singles revealed roughly 30 per cent of women and 21 per cent of men really do compare their current sex lives with the nookie they had with their exes, so it's not necessarily all in our heads.
Regardless, there are few things more destructive to your bond (and in turn, your sex life) than indulging in SCM.
"Going into comparison mode isn't going to turn on your sexual partner. If anything, it will push them away or cause an argument," explains Melbourne-based psychosexual therapist, Christopher Brett-Renes.
And tense conversations and emotional distancing aren't the only things SCM can lead to.
A 2019 study published in the European Journal of Social Psychology found men who focus on their insecurities in a relationship experience a more rapid decline in their sexual desire than those who are secure.
Which makes sense, given scoring your performance against an SO's past isn't exactly conducive to wanting to get it on, or attractive to witness.
Unsurprisingly, research suggests when it comes to our bedroom hang-ups, men are most likely to fixate on how they stack up in the size department, while women fret about how we look and smell, and we all stress about whether we're sufficiently pleasing our partners.
This tendency to home in on what we might be getting wrong, rather than acknowledging what's going right, is actually a common psychological phenomenon referred to as 'negativity bias'.
It's the same reason we often remember a bad date far more vividly than a good one, or pay close attention to a single critical comment on a social media post among a sea of positive feedback.
Simply put, our brains are hardwired to give more weight to negatives; it's their way of attempting to protect us from repeating past traumas.
In essence, this is where sexual comparison stems from – the instinct to avoid being burnt like we've potentially been burned before.
But while it's natural to want to know we're as sexually desirable and satisfying as an ex, Brett-Renes is quick to point out it's largely futile and harmful to bring the topic up.
"People often overlook the fact that an ex is the ex for a reason, it doesn't matter what the sex was like. Don't let your insecurity damage your relationship – your partner IS WITH YOU," he emphasises.
And this is really at the heart of preventing Sexual Comparison Mode from wreaking havoc in your relationship: accepting it's not actually important whether you're the greatest lover your partner has ever had – just that you're the best version of yourself, the person they've chosen to stick it out with.
That said, even the most self-assured of us isn't immune to the odd insecurity freak-out on a bad day (as it turns out, PMS, two months in lockdown and forgoing sleep will do the trick). So long as you don't make sexual comparison the focus of your relationship, it's possible to recover from it.
And speaking from experience, once you've bounced back to your secure self, it never hurts to have make-up sex.
