If you want a happy marriage, should you cohabit first? A compelling question, perhaps, for anyone reading this via clairvoyance in the 1970s. But not for the rest of us: these days, it’s the boringly normal choice, except among certain religious people for whom the issue presumably wouldn’t arise to begin with. Yet over and over, research – including a study published just this September – has linked cohabitation to a higher risk of divorce. Then again, other studies keep finding the opposite, including one published in October, using, amazingly, the same data set as the September one. Far from achieving harmony, it sounds as if the researchers are glowering at each other from opposite ends of the living room, wondering if they’re really going to have to spend the next 40 years of their lives putting up with this crap.

Part of the reason for the discrepancy isn’t about cohabitation, but the kind of people we already are when we decide whether to cohabit. If you’re strictly religious, you’ll be much less likely to move in before marriage, and less likely to split up if things don’t go well. Whereas if you’re the kind of convention-flouter willing to scandalise elderly family members by cohabiting, you’ll surely also be more willing to contemplate divorce. This helps explain why the cohabitation-divorce effect seems to be diminishing with time: nowadays, thanks to changing norms, it’s not just convention-flouters who cohabit, so it’s not just those more prone to divorce who do it. In any case, other research suggests the crucial factor isn’t marriage or cohabitation but age: whichever form of “settling down” you choose, it’s far less likely to work out if you do it very early in adulthood, as opposed to later on.

To the extent that there really is a link between cohabitation and marriage breakdown, though, it probably stems from certain weird psychological aspects of commitment. Cohabiting feels like an easier, lower-commitment option; indeed, it’s often partly a response to economic necessity. But that brings two problems. One is sunk cost bias: once you’ve done the easier thing for a few years, it feels painful to throw away the investment, even if you ought to. The other, some therapists argue, is that cohabitation isn’t very accurate as a trial run at marriage, since every time you bump up against a tension, you needn’t confront it wholeheartedly. Instead, you tell yourself – consciously or otherwise – that it’s just a test, that you’re free to leave anytime. So you avoid a true reckoning with the question of your compatibility, and thereby risk marrying the wrong person.

Fortunately, as Alain de Botton put it in a justly celebrated essay, you’ll marry the wrong person anyway. They’ll refuse to conform to the ideals you project on to them or to shield you from your own craziness; they’ll frustrate your plans for your life, all without malice, simply because they – and you – are human. (Unless they’re malicious, in which case, leave.) “Choosing whom to commit ourselves to is merely a case of identifying which particular variety of suffering we would most like to sacrifice ourselves for,” De Botton concludes. And one of the milestones of adult life, I’d submit, is when you realise this is actually brilliant news.

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Attached, by Amir Levine and Rachel Heller, looks at relationships through the lens of “attachment theory”, arguing that understanding your attachment style – secure, anxious or avoidant – is key to a fulfilling marriage.

oliver.burkeman@theguardian.com