What is loss aversion, and how does it change the way people invest?

What is loss aversion?#

Loss aversion is a pattern in how people judge outcomes: a loss tends to feel heavier than a gain of the same size. Losing $500 can sting more than finding $500 feels good. The idea comes from prospect theory, the work of psychologist Daniel Kahneman and the late Amos Tversky, as described in a 2010 report the Library of Congress prepared for the SEC^[1].

That report sums up the core finding in plain terms: the value function guiding investors is asymmetrical with respect to losses versus gains^[1]. A value function is simply a way of describing how good or bad an outcome feels. Asymmetrical means the two sides are not mirror images. The report adds that excessive risk aversion leads investors to attach more importance to avoiding losses than to achieving gains^[1].

None of this means feeling bad about a loss is irrational. Losses are real, and caution has value. Loss aversion becomes a problem when the urge to avoid the pain of a loss overrides a plan that was built for a long time horizon. Then it can lead to decisions that make the outcome worse, not better.

How does loss aversion show up in a real portfolio?#

Loss aversion rarely announces itself. It can look like a choice that feels sensible in the moment. Three patterns come up again and again in investor education material from U.S. regulators.

Selling in a downturn. A former director of the SEC's investor education office wrote that some initial reactions during a downturn may be to sell and get out of the market^[2]. Selling turns a paper loss into a realized one. If the investment later recovers, the seller is no longer there for it.

Holding losers, selling winners. The SEC's bulletin on investor behavior describes the disposition effect: the tendency of an investor to hold on to losing investments too long and sell winning investments too soon^[3]. The SEC-commissioned report behind the bulletin ties this to loss aversion: loss-averse investors sell high-performing investments hoping to recoup their losses on poor performers but, in fact, achieve the reverse^[1]. The bulletin notes that in the months after the sale, the winners often continue to outperform the losers still held^[3].

Staying too safe for too long. Investor.gov lists a common mistake as putting money that will not be needed for a very long time into investments that pay a low amount of interest, where inflation and taxes can erode buying power^[4]. Avoiding every short-term loss can mean accepting a slow, quiet loss of purchasing power instead.

Why does a loss need a bigger gain to recover?#

Large losses are also hard to undo for a purely arithmetic reason. A percentage loss shrinks the base. The recovery then has to work from that smaller base, so it needs a larger percentage gain just to get back to where you started.

This is one honest reason to care about large losses: they are hard to climb out of. It is also why diversification matters: Investor.gov notes that diversification can help reduce the overall risk of a portfolio^[5], so one holding's collapse does not sink everything. For more on how deep declines are measured, see volatility and drawdowns.

Are market declines normal, or a sign something is broken?#

Declines are part of investing in stocks. Investor.gov notes that large company stocks as a group have lost money on average about one out of every three years^[6]. A down year is common; it does not by itself mean a plan has failed.

FINRA acknowledges the emotional side directly: volatile markets can inspire feelings of fear and anxiety among investors^[7]. Its advice is to avoid impulsive decisions when markets become volatile or economic conditions change, and it notes that solid goals tied to a sound long-term plan typically will survive short-term ups and downs^[7].

There is a second piece of arithmetic worth knowing. Equal percentage moves do not cancel out. A $10,000 balance that rises 20% and then falls 20% ends at $9,600, and so does one that falls 20% first and then rises 20%. This is not a reason to fear every swing. It is a reason to judge risk by the size of possible losses, which is the core of risk and return.

How can you keep loss aversion from steering your decisions?#

The most useful tools are boring ones, set up before a decline rather than during one. The SEC piece on market downturns puts it simply: if you have the right investment plan, you shouldn't need to make rash decisions during times of market volatility^[2].

1. 1

   Write down your goal and time horizon

   Note what the money is for and when you will need it. Money needed in two years and money needed in twenty should not be invested the same way. Our guide to risk tolerance and time horizon walks through this.

2. 2

   Pick an asset mix you can live with in a bad year

   Choose a mix of stocks, bonds and cash that you could hold through a large decline. If a 30% drop in the stock part would make you sell, the mix may be too aggressive for you.

3. 3

   Decide your rules in advance

   Set a schedule for adding money and a rule for rebalancing. FINRA describes dollar-cost averaging as investing equal portions at regular intervals rather than all at once^[7].

4. 4

   Judge each holding on its prospects, not its purchase price

   The price you paid does not affect what an investment will do next. Ask whether you would buy it today. This directly counters the disposition effect.

5. 5

   Pause before acting on fear

   If you feel an urge to sell everything after a drop, wait, reread your written plan and check whether anything about your goal has changed.

What mistakes do beginners make?#

1. Selling everything after a sharp drop

   This turns a temporary paper loss into a permanent realized one and leaves you out of any recovery. Before selling, check whether your goal or timeline has actually changed.

2. Anchoring on the purchase price

   Waiting to "get back to even" before selling a weak holding lets the original price, which the market ignores, drive the decision. Compare the holding with what you would buy today instead.

3. Keeping long-term money in cash to avoid any loss

   Cash avoids price swings but can lose buying power to inflation over long periods. Match the level of risk to when you need the money.

4. Making big changes in the middle of a decline

   FINRA advises avoiding impulsive decisions when markets become volatile. Review your portfolio on a set schedule that matches your plan rather than reacting to each day's move.