The endowment effect: why investors demand more to sell than they would pay to buy
In a rational world, the value of an asset is independent of whether you currently own it. If you would pay £10 for a coffee mug, you should be willing to sell one you own for any price above £10. The endowment effect says this is not how people behave. In the classic experiment by Kahneman, Knetsch, and Thaler (1990), participants randomly given coffee mugs consistently demanded approximately twice as much to sell them as participants without mugs were willing to pay. Merely owning the mug doubled its subjective value. The implication for investing is clear: investors systematically overvalue their existing holdings, making it disproportionately difficult to sell.
Mechanism: loss aversion and ownership
The endowment effect is closely related to loss aversion. Selling an owned asset is psychologically coded as a loss—you are giving something up. Buying an unowned asset is coded as a gain. Because losses feel roughly twice as bad as equivalent gains feel good (as Kahneman and Tversky established in prospect theory), the threshold for selling is higher than the threshold for buying. Ownership activates loss aversion; it transforms an abstract market price into a personal reference point that the seller must psychologically overcome.
How the endowment effect distorts portfolios
In practice, the endowment effect creates several identifiable portfolio distortions. Reluctance to sell losers: investors hold positions that have declined substantially below their purchase price because selling crystallises the loss. This overlaps with the disposition effect and the sunk cost fallacy. Overweighting of inherited or gifted positions: positions received as gifts or through inheritance are retained far longer than their risk/return profile warrants, because selling them does not feel like an investment decision but a personal betrayal. Excessive concentration in employer stock: employees systematically hold too much of their own employer's stock in their retirement accounts, partly because of the endowment effect—the familiarity of ownership inflates its perceived value.
Systematic approaches as a corrective
Rules-based investing directly counteracts the endowment effect by making sell decisions automatic rather than discretionary. A momentum strategy that sells when a security falls below a trend-following threshold does not ask whether the investor feels comfortable selling—it executes. A rebalancing rule that reduces equity exposure when equities exceed a target weight does not negotiate with the investor's attachment to the positions—it acts. For investors who use systematic rules, the endowment effect is constrained to the design of the rules themselves rather than infecting individual sell decisions.
Implications for portfolio review
A practical self-test for the endowment effect is the regret inversion question: would you buy this position at its current price, today, if you did not already own it? If the answer is no, the endowment effect may be causing you to hold a position you would not rationally initiate. This question reframes the decision from "should I sell?" (activating loss aversion) to "should I buy?" (a neutral, forward-looking question). The two questions should have the same answer if you are evaluating the position on its merits rather than your ownership of it.
The endowment effect in pfolio
pfolio's monthly rebalancing executes the trades the rules specify, including reductions in positions the investor would otherwise be reluctant to trim. Because the strategy commits in advance to selling appreciated assets back to target weights and to exiting positions when their momentum signals turn negative, the endowment effect has no point at which it can resist a sale. Allocations the investor has come to feel attached to are still adjusted by the rule. The methodology is documented at how we build portfolios.
Related articles
Disclaimer
Get started now
