The 10 Mistakes Investors Most Commonly Make

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All investors make mistakes. Otherwise, we'd all be millionaires. The trick is figuring out what our investing mistakes are -- and then trying to avoid them.

Meir Statman, one of the nation's leading experts in behavioral finance (the study of why people do irrational things with their money), has written a new book on the topic. In What Investors Really Want, published in October by McGraw-Hill, Statman goes a long way toward helping investors understand that many of their mistakes are caused by their own deep-seated emotions rather than, say, a company's unexpectedly poor earnings.

In an interview with DailyFinance, Statman, a professor of finance at Santa Clara University in California, shared his top 10 errors that trip up average investors:

Meir Statman: What Investors Really Want
Meir Statman: What Investors Really Want

1. Hindsight error. "One of the most pernicious mistakes," Statman says. Because you can see the past clearly, you think you have a similar ability to tell the future. Hindsight error is common at the moment, Statman says, because many people are convinced they saw the crash coming in 2007. In reality, they may have thought a crash was possible, but they also thought the market might continue to zoom upward. Now, investors are convinced they actually saw the problem in 2007 but just didn't act on it. So, they believe wrongly that they can act correctly today. They think they know to sell at the precise moment the market is high and buy when the market is low. Based on their hindsight of 2007, portfolio diversification doesn't protect you from losses. But market timing rarely works, Statman says.

2. Unrealistic optimism. This is loosely related to overconfidence. Psychological studies have shown that when you ask people if they think they have the ability to pick stocks that will have above-average returns, men tend to say yes more often than women. "It's not because men are so smart. It's because men are unrealistically optimistic about their abilities," Statman says. This quality is great for job interviews, where you need to stand out from a crowd, but lousy for investing. "When you are unreasonably optimistic in the stock market, you are just readying yourself for an accident," he says.

3. Extrapolation errors. People expect that trends that existed in the recent past will continue in the future. For example, the fact that gold has gone up for the last 10 years has led many to believe it will always go up. But a study of a longer period -- going back to 1971 when President Richard Nixon ended the gold standard -- shows that gold hit a high of $850 an ounce in 1980 but was selling for $345 as long as 10 years later.

4. Framing errors. Often, Statman says, investing is like a game of tennis. People tend to see themselves hitting a ball against a wall, which seems easy. But that's the wrong frame. Investing is really like playing against another player -- when the other player is Warren Buffett or Goldman Sachs. Investors make framing errors when they see a CEO on TV talking up his stock. If it sounds good and you buy that stock, that's a framing error. Instead, you should be asking yourself: "Who else is watching this program, and what do I know that is uniquely mine?" "The answer is nothing," Statman says.

5. Availability errors. This refers to what information is available in your memory. Investors are often lulled into this error by investment companies. When you see an advertisement for a fund, it's almost invariably for one that has a four- or five-star rating from Morningstar. That way, the one- and two-star funds, with lackluster results, aren't available in your memory. "You say to yourself that there's a 90% chance I will be a winner," Statman says. Instead, look at results of entire fund families -- including the losers, not just the winning funds for a particular period, he says.

6. Confirmation errors. Investors tend to look for information that confirms their hypothesis, but they disregard evidence that contradicts it. Gold bugs, for example, constantly remind us that gold is a good hedge against inflation and a declining dollar. But when confronted with the evidence that gold actually fell price for an entire decade, they dismiss that as a different era because Ronald Reagan changed the rules of the investing game, and that problem won't be repeated.

7. Illusion of control. This is a sense investors have that they can make the market go up or down. It's like gamblers blowing on their dice before rolling. "These investors think they're riding the tiger, when in fact they're holding the tiger by the tail," Statman says. If you think you have a trick that can get the market to go your way, you better think twice: This is the illusion of control. "When you realize the market is actually a wild beast that can devour you, you try to put it in a cage," he says. A much safer approach.

8. Anger. This is an emotion we all know: It leads to things like road rage. In investing, you try to get even with the market. You do such things as double down or even sell all your stocks impulsively. "If you feel angry, it's better to wait 10 days before buying or selling, or you'll regret it later on," Statman says,

9. Fear. The other side of exuberance. When you're afraid, everything looks like a threat, and when you're exuberant, everything looks like an opportunity. Lots of investors are still afraid because of the market crash two years ago. They're sitting on the sidelines in cash earning no return or investing in things like Treasury bills, which aren't much of a bargain. "Risk and return go together," Statman says. "So, if you think the market is risky today, then you should also think the market has a good potential for high returns."

10. Affinity of groups. Also known as herding. You hear from your pediatrician that he's buying gold, so you think you should, too. But what do these people really know? What is the analysis based on? Statman notes that some herds are worth joining and some aren't. Many investors follow Warren Buffett's investment decisions and buy similar stocks. Since Buffett is usually a winner, perhaps that's a herd worth joining. But buying Internet stocks in 1999 or houses in 2005 based on what everyone else was doing was a horrible mistake.

Statman makes no grand conclusions in his book, but he does point out repeatedly that the average investor can rarely beat the market. Therefore, he recommends small investors put their money in index funds that provide average, if not spectacular returns -- and not catastrophic losses

"But if you like the pizazz of investing," he says, you might take a shot on individual stocks. Just be careful.