Endowment Effect: Why Traders Overvalue the Stocks They Already Own

The endowment effect is the habit of valuing something more simply because it is yours. In trading, it shows up as a quiet stubbornness: a stock you bought at ₹400 somehow feels worth more than the same stock sitting on someone else’s watchlist at ₹400. Nothing about the company changed. Only the ownership did.

We all know a trader who has held a position for two years “because it will come back”. Very often the endowment effect is doing the talking. This guide explains where the idea comes from, what the research actually found, how it leaks into Indian trading accounts, and a few practical ways to keep it from deciding your exits for you.

What is the endowment effect?

Psychologists and behavioural economists use the term for a simple finding: people are more likely to keep an object they own than to acquire that same object when they don’t own it. It is also called divestiture aversion, which is a good description of how it feels. Selling feels like giving something up, not like a neutral swap of an asset for cash. (Wikipedia’s summary of the research is a good starting point if you want the academic trail.)

Researchers usually show it in two ways. The first compares prices. Your willingness to pay (WTP) is the most you would spend to buy something. Your willingness to accept (WTA) is the least you would take to sell it once you own it. In a perfectly rational world these two numbers should be roughly equal for the same item. In experiments, WTA tends to come out higher than WTP, even when people have owned the item for only a few minutes and have no reason to be attached to it.

The second way is about swaps. Give people one good and offer them a trade for a similar-value alternative, and many simply hang on to what they were handed first.

The mug experiment

The best-known study is by Daniel Kahneman, Jack Knetsch and Richard Thaler. Cornell University undergraduates were given a coffee mug and then offered the chance to sell it or trade it. The price owners demanded to part with the mug was roughly twice what non-owners were willing to pay for it. Same mug, same classroom, very different valuations depending on who held it.

The three economists wrote up this line of work in a 1991 Journal of Economic Perspectives paper, “Anomalies: The Endowment Effect, Loss Aversion, and Status Quo Bias”. The title itself tells you how closely the three ideas are linked. Thaler had first used the term “endowment effect” back in 1980.

Other studies pushed the gap much further. In work by Ziv Carmon and Dan Ariely on tickets to a US college basketball tournament, people’s hypothetical selling price was 14 times their hypothetical buying price. Those were stated prices, not real trades, but the direction is the same.

Owning a stock doesn’t change its value by a single paisa. It only changes how much it hurts to let go.

Why the endowment effect happens

There is no single agreed explanation, and it helps to know the main candidates because each one points to a slightly different fix.

• Loss aversion. The leading explanation. Selling something you own registers as a loss, and losses weigh more heavily than equal-sized gains. On this view the endowment effect is loss aversion showing up even when there is no risk involved.
• Psychological inertia. Neither buyer nor seller has a precise valuation, so there is a range of prices where nobody feels a strong reason to act. People default to doing nothing, which for an owner means holding.
• Reference prices. Buyers and sellers anchor on different reference points. A seller may think about what the market could pay; a buyer thinks about their own taste and budget.
• Ownership and self. Owning something links it to your sense of self. Research by Carey Morewedge and colleagues found that people who already owned one mug and were asked what they’d pay for a second valued it about as highly as owners who were asked to sell. Both groups valued the mug more than buyers who had none, which points to ownership itself rather than the act of selling.

For traders, the honest takeaway is that it is probably a mix. Part of it is the pain of booking a loss, part is plain inertia, and part is that a stock you researched and bought starts to feel like your idea, your call, your judgement on the line.

It isn’t settled science

Some economists have questioned how robust the effect is. Charles Plott and Kathryn Zeiler, writing in the American Economic Review in 2005, questioned whether the effect exists at all, pointing to subject misconceptions and the experimental procedures used to draw out people’s valuations. That debate matters for academics. For a trader, the practical point survives: if there is any chance your exits are being bent by ownership, it costs very little to build a process that checks for it.

How the endowment effect shows up in trading

In markets the effect rarely announces itself. It hides inside reasonable-sounding sentences.

• “I’ll sell once it gets back to my buy price.” The market doesn’t know or care what you paid. Your cost price is a fact about you, not about the stock.
• Holding inherited or gifted shares untouched for years. Many Indian families have a demat account full of shares someone bought decades ago. Nobody would buy that exact portfolio today, yet nobody wants to sell it either.
• Refusing to rotate. You spot a better setup in another stock but won’t free up capital, because selling what you hold feels like admitting the first trade was wrong.
• Asking a higher target than you’d ever accept as an entry. You wouldn’t buy the stock at ₹520 today, but you won’t sell it below ₹520 either. That gap is your WTP and WTA diverging in real time.
• Averaging down out of loyalty. Adding to a falling position because you “know the company” can be valid analysis. It can also be ownership bias wearing a research hat.

The endowment effect sits close to the disposition effect, the tendency to sell winners too early and hold losers too long. They aren’t the same thing. The disposition effect is about gains versus losses; the endowment effect is about owned versus not owned. In practice they often team up, and the result is a portfolio clogged with old losers.

A worked example: the “would I buy it today?” test

Here is a hypothetical case. The stock, prices and quantities are made up to show the arithmetic; they don’t refer to any real company.

Ramesh bought 200 shares of a mid-cap company, call it ABC Ltd, at ₹450 each. His total cost was ₹90,000. Eight months later the stock trades at ₹360, and his position is worth ₹72,000. He is sitting on a paper loss of ₹18,000, or 20% of what he put in.

Meanwhile, his own research flags another stock, XYZ Ltd, at ₹300, which he rates as the stronger setup. He doesn’t have spare cash. To buy XYZ he would have to sell ABC.

The endowment effect frames this as: “If I sell ABC now, I lock in an ₹18,000 loss.” That framing is the trap. Let’s run the cleaner version.

Now suppose, purely to illustrate, both stocks move 10% over the next few months. If Ramesh holds ABC and it rises 10% to ₹396, his 200 shares are worth ₹79,200. If he switches and XYZ rises 10% to ₹330, his 240 shares are worth ₹79,200. Identical. The rupees don’t remember which stock he owned first.

The point is not that switching is always right. It is that the decision should rest on which stock he would choose with fresh cash, not on where he happened to buy. If ABC still wins that comparison, he should hold it with a clear stop and target. If it doesn’t, the ₹18,000 loss is not a reason to stay. (Charges, taxes and slippage would shift these numbers a little in real life; we’ve left them out to keep the arithmetic clean.)

Ask what you would do with the cash, not what you did with it eight months ago.

Practical ways to beat the endowment effect

1. Run the cash test every month

Once a month, go through each holding and ask: if this position were cash right now, would I buy this exact stock, at this price, in this size? A no doesn’t force a sale, but it should force a written reason for keeping it.

2. Decide the exit before the entry

Ownership bias grows after you buy. Set the stop-loss and the target while you’re still a neutral buyer, and enter them as orders where your broker allows. A rule written before you own the stock is written by the version of you whose WTP and WTA haven’t drifted apart yet.

3. Keep a trading journal with the original thesis

Write down why you bought, in one or two lines, at the time of entry. When the thesis breaks, the journal makes it hard to quietly swap in a new one. Our trading journal template has a column for exactly this.

4. Hide your buy price for a day

Some traders review their portfolio with the average-cost column switched off or covered. Without the anchor, you look at the stock the way a new buyer would: price, trend, fundamentals, nothing else.

5. Size positions so no single loss feels personal

A position that is too big for comfort becomes too big to sell. Sensible position sizing, as covered in our risk management guide, keeps each trade small enough that cutting it is a routine decision rather than an emotional event.

6. Treat inherited and gifted shares as cash

If you received shares instead of money, ask whether you would have bought that portfolio with the same amount of money. The sentimental value is real, but it belongs in your family history, not your asset allocation. If you decide to keep some for personal reasons, label them separately so they don’t muddy your trading results. Check the tax treatment before you sell anything.

The endowment effect and other biases

The endowment effect rarely works alone. Loss aversion makes booking the loss painful. Status quo bias makes doing nothing feel safe. Anchoring ties your judgement to the purchase price. Put them together and you get the most common long-term portfolio problem we see: stocks held not because they’re good, but because selling them feels bad. Our roundup of trading biases that wipe accounts covers the rest of that family.

The fix is boring, which is why it works. Rules set before entry, a written thesis, a regular cash test. None of these make you a better stock picker overnight. They just stop ownership from voting on decisions it has no business in.

Disclaimer: This article is for educational purposes only and is not investment advice. The stocks, prices and amounts in the worked example are hypothetical and do not refer to any real company. Trading and investing in securities involve risk, including loss of capital; consult a SEBI-registered investment adviser before making investment decisions.