The disposition effect: why investors sell winners and ride losers

In 1985, Hersh Shefrin and Meir Statman published "The Disposition to Sell Winners Too Early and Ride Losers Too Long: Theory and Evidence" in The Journal of Finance. They argued that investors evaluate each position relative to its purchase price rather than its current expected return, and that this reference-point thinking causes them to take gains quickly and defer losses indefinitely.

Thirteen years later, Terrance Odean tested the prediction directly. In "Are Investors Reluctant to Realize Their Losses?" (The Journal of Finance, 1998), he analyzed roughly 10,000 discount-brokerage accounts and found that investors realized winning positions at a rate roughly 1.5 times higher than losing positions, even though the winners they sold went on to outperform the losers they kept over the following year. The pattern held across virtually every subgroup he examined and was not explained by tax considerations, rebalancing, or transaction costs.

Follow-up work has reproduced the effect across markets, instruments, and investor types. Brad Barber, Yi-Tsung Lee, Yu-Jane Liu, and Terrance Odean documented it in Taiwanese individual investors ("Is the Aggregate Investor Reluctant to Realise Losses? Evidence from Taiwan", European Financial Management, 2007). Andrea Frazzini found it in mutual fund managers ("The Disposition Effect and Underreaction to News", The Journal of Finance, 2006), showing that even professionals delay selling losers and that this delay produces post-earnings-announcement drift.

The mechanism is reference-dependence: the purchase price becomes the psychological anchor against which gains and losses are evaluated, even though it carries no information about the asset's forward-looking expected return. A position that is down 20% from cost feels like a loss to be deferred. The same position, considered fresh, would either be a buy or not — its purchase price is irrelevant to that decision.

The standard advice — "cut your losses, let your winners run" — has been in print for a century and demonstrably fails to change behavior. The reason is that the disposition effect operates below the level of intent: by the time you are looking at the position, the reference point is already active.

The structural fix is to decide the sell condition before the reference point exists. If, at the moment you enter, you write down the specific evidence that would prove the thesis wrong — and the sell decision is bound to that evidence rather than to the unrealized P&L — then the disposition effect has nothing to grip. You are no longer choosing whether to realize a loss; you are checking whether a pre-committed condition has tripped.

Tensile requires every thesis to declare its invalidation condition at entry, so the exit decision is anchored to the thesis rather than to the cost basis.