Imagine a portfolio with two positions. One is up 20% since you bought it. The other is down 20%. You need cash and decide to sell one of the two. If your decision were based purely on each asset’s future prospects, the purchase price would be irrelevant — the only thing that matters is what you expect to happen from here. Yet most individual investors sell the one that’s up and keep the one that’s down. That pattern is so widespread it has its own name in financial literature: the disposition effect, and it’s one of the reasons the returns individual investors actually earn tend to fall short of what they’d get by simply buying and leaving things alone.
What the disposition effect actually is
The disposition effect is the tendency to sell assets that have gained value and hold on to assets that have lost value, even when rational analysis would suggest the opposite. The term was coined in 1985 by economists Hersh Shefrin and Meir Statman, in a paper that used real investment account data to document a pattern that had long been suspected but never rigorously measured: individual investors realize their gains much faster than they realize their losses.
The key to understanding the bias lies in the word “realize.” As long as you don’t sell, a gain or a loss is just a number on a screen — it doesn’t affect your actual wealth in any final way. The moment you sell, that figure becomes a settled fact. Selling for a profit turns a potential success into a confirmed one, producing immediate, tangible satisfaction. Selling at a loss turns a potential failure — something that could still reverse — into a definitive one, forcing you to admit, with no room left for hope, that the original purchase decision was wrong.
This asymmetry has nothing to do with an asset’s objective prospects. It depends entirely on whether the current price sits above or below the price you paid — a reference point that is completely arbitrary from the market’s point of view, since the market neither knows nor cares what price you got in at.
Why we sell winners and hold on to losers
The most widely accepted explanation combines two psychological mechanisms that are each well known on their own, but that here pull in opposite directions within the same decision.
The first is Kahneman and Tversky’s prospect theory, the same framework that explains loss aversion. According to this theory, people don’t evaluate outcomes in absolute terms but relative to a reference point — usually the purchase price — and the function describing how people perceive gains and losses has a distinctive shape: concave in the domain of gains and convex in the domain of losses. In practical terms, this means that when a position is showing a gain, people tend to become risk-averse and prefer to lock in the gain already achieved rather than risk losing it. When a position is showing a loss, the opposite happens: people become risk-seeking, willing to wait it out in the hope that the price recovers and turns the loss back into a gain, or at least into a breakeven.
The second mechanism is more subtle and has to do with identity and ego. Selling at a loss is a confession, even if only a private one, that a past decision was wrong. As long as the position stays open, that confession can be postponed indefinitely — there’s still a chance, however remote, that the asset recovers and vindicates the original decision. This need to avoid regret and preserve the feeling of having been “right” weighs as much as, or more than, the objective financial math.
Neither mechanism requires bad judgment or lack of intelligence. Both show up with the same intensity in seasoned investors as in beginners, and studies using real trading data find that even professionals with advanced financial training display the same pattern, though somewhat attenuated.
How it shows up in practice
The disposition effect isn’t limited to individual stocks, even though that’s where it has been studied in the most detail. It shows up in many different forms:
Selling part of a diversified portfolio after a moderate rally. Many investors, seeing that a fund or ETF is up 10% or 15%, feel the urge to “take some profit off the table,” even though the original investment thesis — holding the asset for decades — hasn’t changed at all.
Holding on to individual stocks with deteriorating fundamentals. It’s common to hold a stock that has fallen 40% or 50% for years, clinging to the hope of “not selling until I get my money back,” even when the evidence about the company suggests that previous price level is never coming back.
Avoiding an honest look at a losing position. A related manifestation is simply not checking. Many people check their winning positions frequently and avoid looking at the losing ones — a way of postponing the confrontation with the decision to sell.
Justifying the wait with a new story. It’s common for an investor holding a losing position to build a new justification for keeping it — “it’ll recover in the long run,” “it’s still a solid company despite all this” — that wasn’t part of the original purchase thesis but appears afterward, as a way to rationalize inaction.
Selling isn’t just a financial decision. For most people, it’s the difference between being able to tell themselves they were right or that they were wrong.
The real cost: what the evidence shows
The disposition effect carries a measurable cost, one that has been documented across multiple studies using real brokerage account data. The original work by Shefrin and Statman, and the studies that followed over the next three decades, consistently show that the stocks investors sell tend to outperform, going forward, the stocks they choose to keep. In other words, the criterion used to decide what to sell — whether the position shows a gain or a loss, rather than its future prospects — systematically produces worse outcomes than a random selection would.
This pattern has two practical consequences for any portfolio. The first is tax-related: in most tax systems, selling at a loss lets you offset gains from other investments and reduce the year’s tax bill, while selling at a gain triggers an immediate tax liability. The disposition effect flips exactly the order that would be tax-optimal, generating more tax than necessary and leaving available tax savings on the table.
The second consequence involves capital allocation. Every euro trapped in a losing position for purely emotional reasons is a euro that isn’t working in an investment with better prospects. The cost isn’t just the loss already suffered — that’s the same regardless of when you sell — but the opportunity cost of keeping that capital locked into an asset you no longer believe in, purely to avoid the discomfort of closing the position.
How to avoid falling into the disposition effect
As with most cognitive biases, knowing about it isn’t enough to neutralize it completely, but it does make it possible to build systems that reduce its influence over real decisions.
Separate the sell decision from the purchase price. Before deciding whether to sell a position, mentally cover up what you paid for it. The only question that matters is: “Would I buy this today, at the current price, with the information I have now?” If the answer is no, the position should be trimmed or closed, regardless of whether that means booking a gain or a loss.
Define your investment thesis and its exit conditions up front. Writing down, at the time of purchase, what you expect from an investment and what circumstances would make you sell it gives you an objective standard to fall back on later, instead of deciding in the heat of the moment based on what color the position shows on your screen.
Review losing positions with the same frequency as winning ones. If you notice you’re avoiding a look at a particular position, that avoidance is itself information: it probably means you already know, deep down, that it should be sold.
Default to diversified vehicles. Index funds and diversified ETFs reduce exposure to the disposition effect, because there’s no single emotional “story” tied to one specific company. Even so, the bias can still reappear at the level of the overall portfolio, so the rules above remain necessary.
Treat selling at a loss as a tool, not a failure. Selling an asset that no longer makes sense in the portfolio, even at a loss, is a management decision, not an admission of defeat. The real defeat isn’t the loss already baked into the price — it’s keeping capital tied up for longer than reason would advise.
The disposition effect reveals something uncomfortable: a large share of sell decisions have nothing to do with an asset’s future prospects and everything to do with the need to feel good, or avoid feeling bad, about the past. Recognizing it doesn’t remove the impulse, but it does let you tell it apart from a genuine investment judgment — which, in the end, is the only basis on which it makes sense to decide what stays in a portfolio and what doesn’t.
