Your mug is worth double — because it's yours

In 1990, economists Kahneman, Knetsch and Thaler handed out university mugs to half a class, at random. Then they opened a market: mug owners could sell, the rest could buy.

In theory, about half the mugs should have changed hands. In practice, very few did. Owners asked around 7 dollars; buyers offered around 3. Same mug, minutes of ownership — and it was already worth more than double, but only to the person holding it.

That's the endowment effect: owning something inflates its value in our eyes, instantly and for no reason. It's why free returns and 30-day trials are so profitable: once the product is "yours", giving it back hurts.

And it's why your storage room is full. You don't keep things because they're valuable — they feel valuable because you keep them.