Latest / Behavioral Economics with Fexingo: Decision Making, Bias, and How People Really Spend / The Diderot Effect How One Purchase Leads to More
Transcript
- Lucas: If you've ever bought a new coffee table and then suddenly felt like your old rug looked shabby, you've lived today's topic. It's called the Diderot Effect, and it explains why one purchase often pulls a whole string of others along with it. Luna: Diderot — the French philosopher, right? The guy who co-created the first modern encyclopedia. I remember reading somewhere that he wrote an essay about a dressing gown that ruined his life. Lucas: Exactly. Denis Diderot, in 1769, was given a beautiful new scarlet dressing gown by a friend. He was a scholar, lived modestly, but this gown was elegant. And he loved it. But then he sat at his desk and realised his old straw chair looked embarrassingly shabby next to the gown. Luna: So he bought a new armchair. Then a new desk. Then new bookshelves. Then prints for the walls. Within months, his entire study had been replaced. Lucas: He wrote a famous essay called 'Regrets on Parting with My Old Dressing Gown' where he basically says: I was the absolute master of my old dressing gown, but I have become the slave of my new one. The gown cost about 30 livres, by the way. For context, that was several months' rent for a university scholar. It was a luxury item. Luna: And he's rueful about it. The essay is genuinely melancholic. He says his old room felt like home, and the new one felt like a showroom. Lucas: That's the Diderot Effect in a nutshell: a single purchase creates a sense of inconsistency with existing possessions, and we resolve that inconsistency by buying more. Retailers know this intimately. Think about IKEA — their entire store layout is designed to show you a fully styled room. You come in for a $20 lamp, and you leave with a $400 cart because the lamp 'needs' a side table, a rug, a plant. Luna: And it's not just furniture. Apple does this brilliantly. Once you buy an iPhone, the AirPods, the Apple Watch, the charger that works with both — each one makes the others feel more necessary. The ecosystem creates a Diderot spiral. Lucas: Right. The economist Juliet Schor, in her 1998 book 'The Overspent American', documented this pattern in detail. She called it 'competitive consumption' — the idea that we're not just buying things, we're buying a coherent lifestyle. One purchase signals a new identity, and then other goods have to align with that identity. Luna: And it's not always about luxury. Even a new set of kitchen knives can make you feel like you need a better cutting board, nicer pans, maybe a whole kitchen renovation. The effect scales with the purchase. Lucas: That's the key insight. It's not about snobbery — it's about cognitive consistency. We want our possessions to match. And that desire is so strong that it overrides our budget. A 2023 survey from the National Retail Federation found that 62% of Americans said they made at least one unplanned purchase after a major household buy like a sofa or a bed. Luna: That's a huge number. Almost two out of three. And the unplanned purchases averaged around $150 each, so it adds up fast. Lucas: And this is where the Diderot Effect intersects with debt. Think about holidays: you buy a new dress for a wedding, then you need shoes, then a bag, then jewelry. Or moving into a new apartment: you get a sofa, then you need a coffee table, then a lamp, then art. Each purchase feels justified because it completes the picture. Luna: It reminds me of something you said a few episodes ago about the sunk cost fallacy — that we keep spending because we've already spent. The Diderot Effect is almost the opposite: we keep spending because we haven't spent enough to make the first purchase look right. Lucas: That's a great way to put it. The first purchase creates a gap, and we feel compelled to fill it. So what do we do about it? One practical tactic is the one-week rule: after a major purchase, wait at least a week before buying any accessories. That pause gives the initial excitement time to settle, and often the urge to complete the set fades. Luna: I've also heard of a 'matching budget' — you decide in advance that for every major purchase, you'll spend no more than, say, 10% of its value on complementary items. That way you don't spiral. Lucas: That's smart. And there's a deeper question too: 'Does this purchase truly improve my life, or does it just create a new need?' Diderot himself realised, after replacing his whole study, that he actually preferred the old room. It felt like him. The new room felt like a stranger's house. Luna: That's the thing — we often confuse novelty with improvement. A new thing can feel good simply because it's new, not because it's actually better. And then we chase that feeling. Lucas: That desire to 'complete the set' is so powerful that it even shows up in non-material domains. Have you noticed how people who buy one book in a series often feel compelled to buy the whole series? Or how watching one episode of a show can trap you into binging the entire season? Luna: Absolutely. And subscription services exploit that — you buy one class on a platform, and suddenly you're considering the whole bundle because it feels incomplete otherwise. Lucas: So the Diderot Effect is really a specific instance of a broader cognitive bias: the desire for coherence. And once you name it, you start seeing it everywhere. That's the first step to defending against it. Luna: It's also a reminder that consumer culture isn't just about individual products — it's about systems. Retailers design systems that trigger the Diderot Effect deliberately. IKEA's room displays, Apple's ecosystem, even Amazon's 'frequently bought together' — they're all nudging us toward the spiral. Lucas: And to be fair, sometimes the spiral is fine. If you're setting up a home and you have the budget, buying a matching set can be efficient and satisfying. The problem is when it's unconscious and automatic, especially when money is tight. Luna: Right. It's about awareness. Once you see the pattern, you can decide consciously whether to follow it. Lucas: And that's really the goal of this show — to make these patterns visible. If walking through the economy with us has made something click for you, honestly, if today was worth a coffee to you, that's the link: buy me a coffee dot com slash fexingo. Luna: Yeah, listener support is what keeps this ad-free and allows us to spend time on topics like this. It's a small way to say this matters. Lucas: And to bring it full circle: Diderot would probably appreciate that level of mindful consumption. He regretted his new gown not because it was ugly, but because it changed his relationship to everything else he owned. Luna: So next time you're tempted to buy a matching set, take a beat. Ask yourself: am I buying this because I need it, or because it's trying to keep up with the dressing gown? Lucas: That's the question. And if you can answer it honestly, you're already ahead of most of the market.