Investor psychology: the mental traps that cost beginners money

Most beginners lose money in the stock market less through bad luck than through predictable mental habits. Following the crowd, refusing to sell a loser, trading too often and panicking in a fall all have names, and research has measured what they cost.

You can't switch these instincts off. You can write rules in advance that make them harder to act on.

Why your brain works against you

Two findings explain most of what follows.

In 1979, Kahneman and Tversky published prospect theory. One of its findings is that our sense of value is "steeper for losses than for gains": losing USD 1,000 hurts more than gaining USD 1,000 feels good. This is loss aversion.

In 2000, Barber and Odean studied 66,465 US households at a discount broker from 1991 to 1996. The households that traded most earned 11.4% a year, while the market returned 17.9%. The average household earned 16.4% and replaced 75% of its holdings each year. The authors pointed to overconfidence as the explanation.

These studies used US data. The instincts they describe are human, and they show up in every market.

The traps, one by one

1. Herd behaviour and FOMO

What it is. Herd behaviour means buying because everyone else is. FOMO (fear of missing out) is the feeling that drives it.

How it looks. A social media post or chat group shares screenshots of a share that "doubled this month". Members pile in, often after most of the rise has happened. Buying on a tip like this, with no view of the business, is speculation, not investing.

Unlicensed "advisers" and scams use exactly this pressure. In March 2025, IOSCO, the global body of securities regulators, launched I-SCAN. It is a warning portal that brings together alerts from over 150 regulators about unlicensed firms and suspected scams.

Counter-habit. Before acting on any tip, ask: is the source licensed by my country's financial regulator, and can I explain in one sentence why I own this? If either answer is no, don't act on it.

2. Loss aversion: holding losers

What it is. Because losses hurt so much, you avoid "making them real". A share that falls 30% feels like a paper loss as long as you don't sell.

How it looks. You bought at USD 20 and it's now USD 14. You tell yourself you'll sell "once it gets back to 20". Meanwhile the money stays tied up in your weakest idea.

Counter-habit. Ask the fresh-money question: "If I had this cash today, would I buy this share at today's price?" Your buy price doesn't change the answer.

3. Selling winners too early (the disposition effect)

What it is. The flip side of trap 2. Taking a profit feels good, so people sell winners fast and keep losers. Researchers call this the disposition effect.

The evidence. Terrance Odean studied 10,000 accounts at a large discount broker. He found a strong preference for selling winners rather than losers. The shares people kept did not do better afterwards, so the habit didn't pay.

Counter-habit. Decide in your written rules what would make you sell, based on the reason you bought, not on how the price makes you feel.

4. Overconfidence and overtrading

What it is. After a few good trades, you start to believe you can read the market. You trade more and add risk, sometimes by borrowing on margin.

The evidence. In the 2000 Barber and Odean study, the most active traders trailed the market by 6.5 percentage points a year (11.4% vs 17.9%). Each trade also costs commissions, fees and the spread, which add up for frequent traders.

Counter-habit. Count your trades. Set a maximum number per month in your rules, and keep a journal so you can see your real record, not the one you remember.

5. Recency bias

What it is. Treating the last few weeks as a forecast of the next few years.

How it looks. After a strong run, the market feels safe and you put in more than you planned. After a bad week, it feels doomed. Neither feeling tells you much about the future.

Counter-habit. Look at a long chart of a broad stock index, covering many years, before any big decision.

6. Anchoring to the buy price

What it is. Fixing on one number, usually what you paid, and judging everything against it.

How it looks. "It was 20 when I bought, so 14 is cheap." The market does not know or care what you paid.

Counter-habit. In your journal, write down why you own each holding. Review that reason, not the gap from your buy price.

7. Confirmation bias

What it is. Looking only for news that agrees with what you already believe.

How it looks. You follow accounts that are bullish on your holdings and mute anyone who disagrees.

Counter-habit. Before you buy, write down the three strongest reasons it could go wrong. Revisit them each quarter.

8. Panic selling in falls

What it is. Selling everything during a sharp drop to make the pain stop.

How it looks. Say the index you follow drops 4% in a day and headlines call it a crash. Your portfolio is down USD 2,000 since breakfast, and selling feels like the only way to stop it. If you sell, you lock in the loss and still have to decide when to get back in.

Counter-habit. Use a cooling-off rule: no selling on the day of a big fall. Re-read your written plan first.

Worked example: why losses are hard to recover (%)

Losses and gains are not symmetric. If a holding falls by a percentage, it needs a bigger percentage rise to get back to where it started.

Example: you invest USD 10,000 and it falls 30% to USD 7,000. To get back to USD 10,000 you need USD 3,000 more. That is 3,000 ÷ 7,000 = 42.9% of what you have left.

The formula is: rise needed = fall ÷ (1 − fall).

This is one reason diversification matters. A spread of holdings makes one deep loss less likely to sink your whole portfolio.

Summary: bias, what it looks like, counter-habit

Your plan

1. Write your rules before you invest. One page: why you are investing, for how long, how much you can afford to see fall, and what would make you sell.
2. Keep an investing journal. For every trade, note the date, price, amount, your reason and how you felt. Read it every quarter.
3. Set a cooling-off rule. Wait at least 24 hours between deciding to trade and trading, and never sell on the day of a big fall.
4. Limit how often you check prices. Pick a schedule, such as once a week, and mute price alerts and tip groups.
5. Check every source of advice. Look the person or firm up on your financial regulator's public register, and search IOSCO's I-SCAN warnings.
6. Automate the boring part. Investing a fixed amount each month, known as dollar-cost averaging, takes some decisions away from your mood.
7. Review once a year. Compare your results against the index, after fees, using your journal rather than your memory.

Try it with your numbersInvestment GrowthSee how investing a fixed amount every month could grow your wealth over time.

What to watch out for

• Screenshots of profits. You see the winners people choose to post, not their losses.
• Urgency. "Buy before tomorrow" is a pressure tactic, not analysis.
• Unlicensed advice. A big following is not a licence. Regulators regularly warn about unlicensed advisers on social media.
• Borrowing to invest. Margin magnifies losses as well as gains, and a 50% fall needs a 100% rise to recover.
• Thinking you're immune. Knowing these biases doesn't remove them. Written rules work better than willpower.