Insights · Letter No. 8 · Behavior
Seven behavioral mistakes that cost investors most
The largest gap between what investments earn and what investors keep is usually behavior. A field guide to our own minds.
Investment returns and investor returns are not the same. Morningstar's annual Mind the Gap study compares the returns funds report with the returns their investors actually earned, given when they bought and sold. In recent editions the gap has been roughly one percentage point a year, largely from poorly timed buying and selling. Here are the habits behind that gap.
1. Loss aversion
Psychologists Daniel Kahneman and Amos Tversky found that losses feel roughly twice as painful as equal gains feel good. That asymmetry makes us sell in downturns to stop the pain, and cling to losing positions to avoid admitting a loss.
2. Recency bias
We assume whatever just happened will keep happening. After a strong year, stocks feel safe; after a crash, they feel dangerous. Both feelings tend to be strongest at the wrong moments.
3. Overconfidence
Most people rate themselves above average at driving, and at investing. Overconfidence leads to concentrated bets and frequent trading. Research by Brad Barber and Terrance Odean on tens of thousands of individual investors' trading accounts found that the most active traders earned noticeably less than those who traded least.
4. Herding
When everyone is buying a hot stock or coin, joining feels safe. By the time an idea is a dinner-table topic, much of its good news is often already in the price.
5. Anchoring
We fixate on an arbitrary number, often the price we paid, and decide based on it. The market does not know or care what you paid. The only relevant question is what the investment is worth now versus its price now.
6. Market timing
Trying to jump out before declines and back in before rebounds requires being right twice. Some of the market's best days have historically come close to its worst, so stepping out can mean missing the recovery.
7. Checking too often
Daily prices are noisy. The more often you look, the more often you see a loss, and the more tempted you are to act. Many patient investors check their long-term portfolios a few times a year, not a few times a day.
Building guardrails
- Write a one-page plan: your goals, your mix, when you will rebalance.
- Automate contributions so investing does not depend on mood.
- Add a 48-hour rule before any unplanned trade.
- Judge decisions by the process, not by one outcome.
This letter is general education, not a recommendation to buy or sell any security. Consider your own situation, and a licensed professional, before making financial decisions.