Hindsight Bias

Hindsight bias is the tendency, after something has happened, to imagine that the outcome was far more predictable than it actually was. In English it's also called the 'knew-it-all-along effect.'

There are two key points. First, once you know the outcome, you feel it was 'obvious all along.' Second, even your memory of how you actually thought before the event slyly shifts.

In other words, this isn't simply a habit of showing off; it's closer to a memory illusion in which our brain automatically overwrites the record of past judgments to match the outcome.

The moment you say 'I knew this would go up' or 'the crash was obvious' after the market rises or falls is exactly this bias at work. The problem is what comes next.

First, it feeds overconfidence. Once the illusion that 'I'm good at reading the market' sets in, it easily leads to reckless bets or overtrading.

Second, it blocks learning. If you rationalize an outcome as 'obvious,' you stop reviewing what grounds you actually used at the time to judge. You lose the ability to distinguish being right by luck from being right by skill.

Third, it leads you to underestimate risk. If you rewrite your memory to 'I knew all along it would recover,' the fear and uncertainty you actually felt in the middle of that crash get erased.

After the 2008 global financial crisis had passed, many people said 'the housing bubble was obvious to anyone.' But various studies reveal that in the run-up to the crisis, in 2004–2007, most experts also failed to predict it. 'Everyone knew' is a narrative constructed only after the outcome was known.

The numbers make the fear even clearer. The S&P 500 fell about 57% from its October 2007 peak (about 1,565) to its March 2009 trough, and this decline stretched over about 17 months.

It's easy now to say casually 'I knew it would recover,' but the pain of that drawdown — holding on for over a year with your assets cut in half — is exactly the part that hindsight bias wipes clean.

This bias is hard to eliminate, but you can suppress it considerably by keeping records.

First, when you make a decision, write down in advance 'why I judged this way' and 'the probability I expect.' Even if your memory shifts after the outcome appears, your true thinking at the time remains.

Second, write down the 'opposite scenario' too. If you note not only reasons to rise but also reasons to fall, there's less room for the 'I knew it' illusion to creep in later.

Third, review process and outcome separately. A good outcome often masks a bad decision, and a bad outcome often masks a good one.

'The Return of Almost Everything' is a site made precisely to show this 'actual history' as it was. When you check for yourself how much an asset fell in a given crisis and how long you had to endure the loss, you can remember the past with real numbers instead of the 'I knew it' illusion.