Loss Aversion and Prospect Theory

Try this before reading further. Choice one: a guaranteed gain of ₹5,000, or a coin toss that pays ₹10,000 or nothing. Most people take the sure ₹5,000. Choice two: a guaranteed loss of ₹5,000, or a coin toss that costs you ₹10,000 or nothing. Most people now take the coin toss. The expected value is identical in every option. The only thing that changed is whether the outcome is framed as a gain or a loss.

That flip is the core of prospect theory, Kahneman and Tversky's model of how people actually decide under uncertainty. It explains why you hold a falling stock for years, why you sell a rising one in weeks, and why so many traders who are down for the month reach for the cheapest, riskiest option on expiry day. I see the same flip on trading desks and in retail accounts. The size of the account does not change it.

Prospect Theory, the actual model

Prospect theory was published in 1979 and refined in 1992 as cumulative prospect theory. It replaced the textbook expected utility model with a description of real behaviour. Four features matter for investors.

• Reference point: you judge outcomes as gains or losses against a reference, usually what you paid, not against your total wealth. A stock bought at ₹500 and now at ₹450 feels like a loss, even if ₹450 is a fair price.
• Loss aversion: losses weigh more than gains. The 1992 paper estimated the ratio at 2.25. Losing ₹10,000 feels roughly as bad as gaining ₹22,500 feels good.
• Diminishing sensitivity: the first ₹10,000 of gain or loss moves you more than the tenth. This makes people cautious with gains and willing to gamble with losses.
• Probability weighting: people overweight small probabilities. A 2% chance of a big payout feels bigger than 2%. That is the psychology of a lottery ticket, and of a far out of the money option bought on expiry morning.

How loss aversion destroys Indian investor returns

Loss aversion shows up in two habits that work against each other, and together they quietly rebuild your portfolio in the wrong shape.

Holding losers too long

Say you buy shares of a large private bank at ₹1,800 and they fall to ₹1,500. Selling now makes the ₹300 loss real. Holding keeps it on paper. So you hold. If the reason you bought has broken, the stock can keep falling, and the money stays locked in it instead of working somewhere else. Prospect theory predicts this: in the loss zone, people become risk seekers. They prefer the gamble of waiting over the certainty of booking the loss.

Selling winners too early

Now say you buy an IT services stock at ₹1,400 and it rises to ₹1,700. The urge to "lock it in" is strong, because in the gain zone people become risk averse. You sell. If the business keeps compounding, you have kept the small win and handed the big one to someone else.

Do both for a few years and the portfolio fills up with the stocks you could not bear to sell and empties of the ones you could not wait to sell. Odean's 1998 study of 10,000 brokerage accounts found exactly this: investors realised gains about 1.5 times as readily as losses, and the winners they sold went on to beat the losers they kept by about 3.4 percentage points over the next year. Module 8.5 covers that study in detail.

The break even trap

Loss aversion has a mathematical accomplice. A fall needs a bigger rise to recover, because the rise starts from a smaller base. The table uses real 2026 numbers.

The Smallcap 250 has nearly made that 35.4% back. It closed at 18,527.20 on 8 September 2026, 34.7% above the low and 0.5% short of the record, though on 12 October 2026 it was still 4.6% below. Investors who sold in March 2025 to stop the pain locked in the 26.1% and missed the 34.7%.

The trap is the urge to get back to even fast. Thaler and Johnson's 1990 experiments found that people who have lost money often take bets they would normally refuse, if the bet offers a chance to break even. In Indian markets that urge has a favourite instrument: the short dated option. SEBI's August 2026 study found that 59% of index options turnover in FY26 happened on expiry day itself, and 97% within a week of expiry. Options produced 92% of individual traders' aggregate losses, and 87.7% of individual options traders lost money in FY26, against 66.0% in futures.

The reference point problem, why purchase price is a trap

For most investors the reference point is the purchase price of each holding. From a finance point of view that number is irrelevant. The stock does not know what you paid. The market does not care. The only live question is whether this is the best use of this money from today's price.

Yet the purchase price colours everything. A stock bought at ₹1,000, now at ₹600, with a broken business, becomes "a temporary loss to ride out". A stock bought at ₹500, now at ₹600, with earnings still rising, becomes "a profit to book". Rationally the two decisions should be made on the same test. Emotionally they are made on opposite tests.

The mental accounting trap

Mental accounting is Thaler's term for treating money differently depending on where it came from or which "account" you file it in. With loss aversion it causes three classic errors.

• House money: treating profits as "not really mine" and taking bigger risks with them. A rupee of profit buys exactly as much as a rupee of salary.
• The temporary account: parking a losing stock in a mental drawer labelled "long term" so you never have to look at it.
• Refusing tax help: not selling a loser even when booking the loss would cut your tax, because selling makes the loss "real".

Worked example: what refusing to book a loss costs

In FY27 you sell a stock held for eight months at a gain of ₹80,000. Short term capital gains on listed equity are taxed at 20%, so the tax is ₹16,000 before cess. You also hold another stock bought six months ago, now ₹50,000 under water, and you no longer believe in it.

Loss aversion in Indian retail data

SEBI's F&O studies give an unusually clear view of the pattern. In FY26 the average loss among individual loss makers was ₹1.47 lakh, while the average profit among profit makers was ₹1.22 lakh. Losses were 21% larger than profits. That is what a book looks like when small gains get taken quickly and losing positions are held, rolled or doubled.

The same study shows the asymmetry in futures. Individuals made money in futures in rising quarters, ₹3,741 crore in Q1 FY25 when the Nifty rose 7%. They lost far more in falling quarters: ₹8,081 crore in Q4 FY26 when the Nifty fell about 15%. SEBI notes that losses in market declines were substantially larger than profits in comparable rallies.

Two field tested defences

Reading about loss aversion does not cure it. Two structural fixes have research behind them.

Look less often. Benartzi and Thaler's 1995 paper on myopic loss aversion showed why. Over short windows, an equity portfolio shows a loss on a large share of days, close to half. Over a year, far fewer years are negative; over five or ten years, fewer still. Each look at a red number is a small dose of loss pain. Investors who look daily feel many more losses than investors who look quarterly, for the same underlying return, and experiments show they then hold less equity. In the 24 months to September 2026, a weak stretch for Indian large caps, the Nifty 50 closed lower on 252 of 487 trading days. A daily checker felt every one of them.

Decide before the moment. Write the rule when no position is live: "I exit when the reason I bought is no longer true", or "I rebalance on the first Monday of every quarter whatever has moved". The decision gets made calmly. The execution is mechanical. That is the whole premise of systematic investing, applied to a behavioural problem.

Common mistakes

• Waiting for break even. The market has no memory of your entry. "I will sell when it gets back to my price" is a rule written by loss aversion.
• Treating a stop as a defeat. A pre set exit is risk control, not a confession.
• Swapping a loss for an option bet. The urge to win it back fast is strongest right after a loss. SEBI's FY26 numbers show how that usually ends.
• Ignoring tax set off. Booking a loss you would exit anyway can lower your tax in the same financial year.

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