Hindsight Bias: The 'I Knew It All Along' Problem in Investing

David Beckham said “Hindsight is a wonderful thing.” Chapter 9 is the last of the belief perseverance biases in Pompian’s book, and it might be the most relatable one. Because we all do this. Every single one of us.

“I Knew It All Along”

Hindsight bias is the impulse that makes you say “I knew it all along” after something happens. Even when you didn’t know. Even when nobody knew.

Here’s the thing. Once an event happens, your brain immediately starts rewriting history. The event that just happened now seems obvious. Inevitable. “Of course that was going to happen.” But before the event, you had no idea. You just forgot that you had no idea.

Pompian explains why this happens. Actual outcomes are concrete. Your brain can grasp them easily. But the infinite number of outcomes that could have happened but didn’t? Those are abstract. Your brain discards them. So the thing that actually happened looks like the only thing that could have happened.

This is not just a thinking error. Your memory literally changes. Research by Baruch Fischhoff showed that when people are told the answers to trivia questions and then asked to recall their original guesses, they consistently remember their guesses as being closer to the correct answer than they actually were.

Your brain is rewriting your memories to make you look smarter than you were.

The Bubble Everyone “Predicted”

Pompian gives the perfect example. In 1998 and 1999, almost nobody called the stock market a bubble. Even sophisticated investors were saying “it’s different this time.” The bull market of the 1990s seemed like it would last forever.

Then it crashed. And suddenly everybody knew it was coming.

“Wasn’t it obvious we were in a bubble?” people say now. No. It was not obvious at the time. If it was obvious, why didn’t you sell everything before the crash?

Pompian wrote the first edition of his book in 2006, when it was “inconceivable to most people that housing could be an unsafe investment.” By 2011, when the second edition came out, everyone was an expert on housing bubbles. “Of course housing was overvalued. It was clearly in the cards.”

No it wasn’t. Not to you. Not in 2006. You just think it was because hindsight rewrote your memory.

I watched the same dynamic in the post-Soviet economic turmoil. After every currency crash, every policy disaster, people would say they saw it coming. Nobody saw it coming. But everybody remembers seeing it coming.

Why This Is Dangerous

The biggest danger of hindsight bias is that it gives you a false sense of your own predictive powers. If you “knew” the last bubble was going to pop, then surely you will know when the next one will pop too, right?

Wrong. You didn’t know. Your brain just convinced you that you knew. And now you are making future decisions based on a predictive ability that doesn’t exist.

This leads to excessive risk-taking. If you believe you can see the future, you bet bigger. You concentrate your portfolio. You time the market. And eventually, you lose.

Four Investment Mistakes

Pompian lists four specific problems caused by hindsight bias:

1. Rewriting history on winners. Your investment goes up. You remember yourself as having predicted this. You forget all the uncertainty you felt at the time. This makes you overconfident in your next investment. The dot-com bubble was full of people who had a few wins and suddenly believed they were investment geniuses.

2. Blocking out memories of losers. Your investment goes down. Instead of analyzing what went wrong, you just… forget about it. You block the memory because it is embarrassing. But here’s the problem. If you don’t remember your mistakes, you can’t learn from them. You will make the same mistakes again.

3. Unfairly blaming fund managers. After a market cycle, everything looks inevitable in hindsight. So when your fund manager underperforms, you think: “How could they not have seen this coming?” But they couldn’t see it coming. Nobody could. Good managers who implement sound strategies will still underperform in certain market conditions. Small-cap value managers in the late 1990s got a lot of criticism, but they weren’t bad managers. Their style was just out of favor.

4. Unfairly praising fund managers. The flip side. When your manager does well, hindsight makes it seem like they were brilliant. But maybe they just happened to be in the right asset class at the right time. You confuse luck with skill because hindsight makes everything look intentional.

The Baseball Analogy

There is a great analogy in this chapter comparing fund evaluation to baseball history.

Before 1900, there was no concept of relief pitching. Pitchers were expected to throw complete games. The only way to measure them was wins and losses.

Then relief pitching was introduced, and earned run average (ERA) became a metric. If you went back and calculated ERA for pre-1900 pitchers, they would look terrible compared to modern pitchers. But that is unfair. ERA didn’t exist as a concept when they played. They were pitching under completely different conditions.

The same principle applies to fund managers. Value investing as a recognized strategy didn’t really exist until Fama and French published their famous paper in 1992. So judging a value manager’s track record from 1980 to 2004 against a value index is unfair for the pre-1992 portion. The manager didn’t know about the value factor. Nobody did. Hindsight makes it seem like the strategy was obvious all along, but it wasn’t.

Cooper, Gutierrez, and Marcum researched this exact problem and concluded that “the current notion of predictability in the literature is exaggerated.” In simpler words: things look more predictable in hindsight than they are in real time.

What To Do About It

Pompian’s advice focuses on honest self-examination.

For wins: when an investment goes up, resist the urge to take credit. Ask yourself honestly: did I predict this for the right reasons? Or did I get lucky? If your reasoning was wrong but the outcome was right, you need to understand that. Lucky outcomes create dangerous overconfidence.

For losses: force yourself to examine failures. Don’t block them out. What went wrong? What did I miss? This is uncomfortable work but it is the only way to actually improve as an investor.

For evaluating managers: understand that markets move in cycles. A good manager sticks to their strategy through good times and bad. Don’t fire a value manager because value was out of favor for a year. Don’t worship a growth manager because growth happened to be hot. Look at the strategy, not just the returns.

For your own humility: remember that even the smartest people in the room didn’t see the last crash coming. The 2008 financial crisis, the dot-com bust, every major market disruption caught the majority of experts by surprise. If they couldn’t predict it, you probably can’t either. And that is okay.

The past looks clear because you already know what happened. The future is uncertain because you don’t. Never confuse the clarity of hindsight with the fog of real-time decision making.

This chapter closes Part 2 of the book, which covered all six belief perseverance biases. If I had to summarize the entire section in one sentence: your brain is an unreliable narrator, especially when it comes to money. The sooner you accept that, the better your investment decisions will be.

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This is part of a series retelling “Behavioral Finance and Wealth Management” by Michael M. Pompian. Start from the beginning.