Sometimes it’s nice to learn that a psychological phenomenon has a name, if only so I no longer have to think of it as Me Being Uniquely Irrational And Self-Defeating. So it is with the Diderot effect – which, I learned recently (via Lifehacker), is the term for when you buy something new, but then it makes your other possessions look timeworn by comparison, so you end up replacing them, too. The inspiration here is Denis Diderot’s 1769 essay Regrets For My Old Dressing Gown, in which he recounts being given a luxurious replacement. “My old robe was one with the other rags that surrounded me,” Diderot laments. But “all is now discordant”. Before long, he’s obliged to replace his furniture and paintings as well: “I was the absolute master of my old robe. I have become the slave of the new one.”

You already knew, of course, that consumerism exploits psychological weaknesses to get us to buy stuff we don’t need. We fall victim to “hedonic adaptation” (the way new possessions become part of the backdrop), along with “upward social comparison” (if you succeed in keeping up with the Joneses, you’ll just pick new Joneses to try to keep up with). But the Diderot effect adds a twist. We use possessions to help construct our identities, and we need those identities to feel consistent. A consistently shabbily dressed person might be signalling that her mind’s on higher matters; a consistently smart one that she values good taste. But someone who’s a random mixture of both just seems weird. In the words of the anthropologist Grant McCracken, products are deliberately marketed in “Diderot unities” – groups whereby, once you’ve purchased one, you’ll feel you need the others. Now that you’re ordering that new dining table from the catalogue, shouldn’t you consider those glasses and plates, too?

It’s too easy to condemn this merely as manipulation. The Diderot effect works because we invest possessions with so much symbolic power. We view certain items – in another McCracken phrase – as “bridging goods” that connect our lives now to our hoped-for futures. You want that Smeg fridge because it expresses something about who you want to be (such as: sufficiently well-off to care about nice fridges). So you buy it, but then the Diderot effect kicks in. And soon you find you’ve accumulated many of the signifiers of the life you dreamed of, without the thing – in this case economic security – they were supposed to signify.

“If there’s something you really want but don’t actually need,” writes the economist Juliet Schor, “there’s a good chance that a recurring symbolic fantasy is attached to it. A faster computer? The dream of getting more work done. A remodelled kitchen? The hope of eating proper family dinners… Laying bare the fantasy illuminates the often tenuous link between the product and the dream.” The Diderot effect hurts your bank balance, but even if it didn’t, it would still be futile, because the things we’re really looking for can’t be got that way. Diderot, in his dressing gown, was chasing a wild goose.

oliver.burkeman@theguardian.com