Thinking Like a Trader

The foundational ideas of prospect theory are that we evaluate outcomes relative to a reference point, and that losses loom larger than corresponding gains. Real‑world observations bear out the power of these concepts. For instance, a study of Boston condominiums during a housing downturn found that owners who had purchased at higher prices—and thus faced larger losses relative to their reference point—set higher asking prices, took longer to sell, and ultimately received more money than owners with lower reference points. A rational agent would ignore the irrelevant purchase price and focus only on current market value. Humans, however, treat a sale below the reference point as a loss, and they resist it.

This asymmetry between what we demand to part with something and what we would pay to acquire it is the hallmark of the endowment effect. In a classic experiment by Richard Thaler and others, participants who were given a mug were later offered the chance to sell it or trade it for an equally valued pen. Owners typically demanded roughly twice as much compensation to give up the mug as non‑owners were willing to pay to obtain it. The source of this gap is loss aversion: owning an item makes giving it up feel like a loss, so we require extra compensation. The effect is not limited to physical goods. A study of Super Bowl ticket lotteries found that 94% of winners said they would not pay $3,000 for a ticket they did not own—yet 92% would not sell their own ticket for that price.

The account describes studies in which selling a possession engaged regions associated with aversion, including the insula and amygdala, while buying engaged reward-related regions such as the ventral striatum. Such findings can be consistent with an emotional response to giving up a possession, but activity in a brain region does not uniquely identify a particular feeling.

The endowment effect is robust but not universal. It is strongest for goods that are unique or personally meaningful, and weaker—or even absent—for goods that are easily substitutable or viewed purely as instruments for future exchange. Its very sensitivity to context, however, demonstrates that reference points are labile. Jack Knetsch’s experiments showed that participants exhibited the endowment effect only when they had physical possession of the object for a while before trading was discussed; merely knowing they would receive it was not enough. More dramatically, market experience can reshape the reference point entirely.

The experimental economist John List studied traders at baseball card conventions and found that novice traders were reluctant to part with cards they owned, but experienced traders showed no such reluctance. In one striking demonstration, List offered convention attendees a small gift for completing a survey: a coffee mug or a chocolate bar of equal value, assigned at random. As they were leaving, he told each person they could swap their gift for the other if they wished. Only 18% of inexperienced traders chose to exchange—consistent with a strong endowment effect—but 48% of experienced traders did so, essentially showing no reluctance at all. One way to describe the experienced traders’ approach is to ask: “How much do I want to have this mug, compared with other things I could have instead?” That framing treats keeping the item as a choice among alternatives. The trading results suggest that the ownership gap can shrink with experience in this setting; they do not establish that experienced traders are indifferent to giving up personally meaningful possessions.

People living in poverty may face a different sort of “trader” problem: spending on one necessity can mean giving up another. Prospect theory offers a way to describe choices made below a reference point, where additional money may feel like a reduction of loss. That framing can illuminate difficult tradeoffs without implying that every person living in poverty experiences every outcome as a loss.

Cultural context also shapes the endowment effect. For instance, the large gap between buying and selling prices consistently found in studies with American students is markedly smaller among English students, hinting that attitudes toward money and minor luxuries vary significantly across societies. Much about the endowment effect and its boundaries still remains to be understood.