Why We Buy Things We Never Needed

How One Scarlet Robe Changed Everything

The famous French philosopher Denis Diderot spent most of his life in poverty. That changed in 1765.

At the age of 52, Diderot faced a financial challenge: his daughter was about to be married, and he could not afford her dowry. Despite his lack of wealth, he was widely respected as the co-founder and principal writer of the Encyclopédie, one of the most ambitious intellectual projects of the Enlightenment.

When Catherine the Great, Empress of Russia, learned of his predicament, she offered to purchase his personal library for £1,000—a fortune at the time. Overnight, Diderot found himself with money to spare.

Shortly thereafter, he bought a luxurious scarlet dressing gown.

hat’s when everything began to unravel.

In his essay Regrets on Parting with My Old Dressing Gown, Diderot reflected on the unexpected consequences of this purchase:

“I was the absolute master of my old robe. I have become the slave of the new one.”

His old robe had fit naturally into his modest surroundings—a straw chair, a wooden table, a few books resting on rough planks, and simple prints hanging on the walls. Together they formed what he called a “harmonious indigence.”

The new scarlet robe changed everything.

Suddenly, his old possessions looked shabby and out of place. The contrast bothered him. The rug seemed inadequate. The chair looked worn. The furniture no longer matched the elegance of his new garment.

One purchase triggered another.

The old rug was replaced with one from Damascus. A large mirror appeared above the fireplace. The straw chair gave way to a leather one. Sculptures and decorative pieces filled the room. What began as a single luxury purchase evolved into a cascade of spending.

His wealth could not keep pace with his new desires.

Today, psychologists and behavioral economists refer to this phenomenon as the Diderot Effect—the tendency for one new possession to create a spiral of consumption. We buy something new, and suddenly everything around it feels outdated. The new purchase creates a new standard, and we spend more time, money, and energy trying to maintain consistency with that standard.

The Diderot Effect is everywhere.

A new phone leads to new earbuds, a new case, and a new watch. A new house triggers renovations, furniture upgrades, and endless decorating projects. A promotion leads to a more expensive car, a larger home, and a higher-cost lifestyle.

The danger is not the purchase itself.

The danger is allowing possessions to dictate our desires rather than letting our values guide our choices.

Diderot eventually recognized the trap he had fallen into and left us with a timeless warning:

“Let my example teach you a lesson. Poverty has its freedoms; opulence has its obstacles.”

More than 250 years later, his lesson remains relevant.

The question is not whether we can afford something.

The question is whether owning it will make us the master of our possessions—or their slave.