Disposition Effect

The disposition effect was named and formally documented by Hersh Shefrin and Meir Statman in their 1985 paper 'The Disposition to Sell Winners Too Early and Ride Losers Too Long.' It represents the market-level expression of loss aversion and mental accounting operating simultaneously in individual portfolios.

The mechanics are straightforward. When a stock rises above the purchase price, the investor experiences an unrealized gain. Selling crystallizes that gain, delivering a burst of positive reinforcement. Holding exposes the investor to the risk that the gain evaporates — a prospect loss aversion makes feel catastrophically bad. The psychologically comfortable action is to sell and bank the win.

Conversely, when a stock falls below the purchase price, selling would crystallize a loss and trigger the pain of loss aversion. Holding preserves the hope — even if fading — that the stock will recover to breakeven. The investor is, in effect, buying a lottery ticket on a recovery rather than making a rational forward-looking decision.

The financial consequences are significant. Numerous studies using US brokerage account data have confirmed that individual investors systematically sell their winners and keep their losers. Terrance Odean's 1998 study of 10,000 brokerage accounts found that stocks investors sold outperformed stocks they held by roughly 3.4 percentage points over the following year — meaning investors systematically dumped their best-performing future holdings.

Tax considerations add a layer of complexity. Selling losers generates tax-loss harvesting benefits in taxable accounts, while selling winners triggers capital gains tax — creating a tax incentive to do exactly what the disposition effect already pushes investors toward (hold winners longer) and the opposite with losers. Yet despite this rational tax incentive to sell losers, the disposition effect often overwhelms tax-efficient behavior in practice.