Outcome Bias: Why a Good Result Doesn't Mean It Was a Good Decision

Imagine a fund manager who concentrated her entire portfolio into 15 stocks, made two huge winning bets, had four terrible losers, and ended up beating her benchmark by 6% per year over five years. Impressive track record, right? Most investors would look at those returns and throw money at her.

But here is the problem: that result was mostly luck. The process was terrible. A concentrated portfolio with wild swings is not a sound investment strategy, it is gambling that happened to work. But because the outcome was good, people judge the decision as good.

This is outcome bias, and Chapter 15 of Pompian’s book makes a case for why it might be one of the most practically dangerous biases in investing.

Outcome vs. Process

The core idea is simple. Outcome bias means people judge decisions based on what happened after the decision, not based on the quality of the decision-making process itself. A good outcome? Must have been a good decision. A bad outcome? Must have been a bad decision.

But anyone who has ever played poker knows this is nonsense. You can make the mathematically perfect play and still lose the hand. You can make a terrible play and still win. Over one hand, luck dominates. Over a thousand hands, skill shows up. But people do not evaluate a thousand hands. They look at one result and draw conclusions.

Pompian references the work of Jonathan Baron and John Hershey from the University of Pennsylvania, who ran experiments where they gave subjects descriptions of decisions made under uncertainty, along with the outcomes. Some were medical decisions, others were about monetary gambles.

The result was clear: subjects rated the decision-making as better when the outcome was favorable, even when they had all the information about the decision-making process. When asked directly, subjects agreed that outcomes should not affect their evaluation of the decision quality. But they did it anyway. They could not help themselves.

The Car Rolling Down the Hill

There is a fascinating study by Elaine Walster from the University of Hawaii that Pompian highlights. She presented subjects with a scenario about a parked car that rolled down a hill. In one version, the car hit a tree stump and caused minor damage. In another version, the car rolled all the way down and caused serious damage. People were asked to rate how much responsibility the car owner bears.

Same event. Same circumstances. Same parked car. But people assigned more blame when the outcome was severe. The owner of the car did the exact same thing in both cases (parked the car), but the worse outcome made people think it was a worse decision.

For investors, this means we ascribe more meaning to dramatic outcomes. A fund manager who has a spectacular year gets treated like a genius. One who has a catastrophic year gets treated like an idiot. Even if their processes were identical and only luck separated them.

Three Ways Outcome Bias Hurts Your Investments

Investing in funds you should not. This is the most common manifestation. You see a fund with amazing five-year returns and you invest. But you never asked: how were those returns generated? Did the manager take enormous concentrated bets? Was the strategy repeatable, or did the manager just happen to be in the right sector at the right time? High returns can come from high risk, and high risk eventually catches up with you.

Avoiding funds you should not. The reverse is equally damaging. A solid fund manager with a sound, disciplined process might underperform for a year or two because their strategy was temporarily out of favor. Outcome-biased investors see the bad numbers and run away, missing out on the eventual reversion to strong performance. Studies show that managers with strong 10-year track records can underperform for one, two, or even three years and then come back strong. But outcome bias makes investors bail at exactly the wrong time.

Chasing overvalued asset classes. When gold is up 30% in a year, or housing prices are climbing fast, outcome-biased investors pile in based on the recent result. They do not ask whether the asset class is overvalued. They do not look at historical price cycles. They just see the big positive number and assume it will continue. This is how people buy at peaks and then watch their money shrink.

How to Fight Outcome Bias

Pompian’s advice centers on one key principle: focus on process, not results.

When evaluating a fund manager, do not just look at the return number. Ask these questions:

How many positions are in the fund? If it is way fewer than the benchmark, that is a concentrated bet, not a strategy.

How many of those positions actually contributed to returns? If two stocks carried the whole fund, that is luck, not skill.

What is the tracking error and R-squared relative to the benchmark? These numbers tell you how much the manager’s returns are explained by the benchmark versus by active decisions.

What is the annualized standard deviation? If it is much higher than the benchmark, the manager is taking more risk than you think.

Sometimes you will find a manager with a sound strategy who has simply been unlucky for a couple of years. The process is good but the outcomes have been poor. Outcome bias tells you to run. Rational analysis tells you this might actually be a buying opportunity.

The same logic applies to your own investing decisions. When something works out, resist the urge to pat yourself on the back. Instead, examine whether your process was sound. Did you research properly? Was your position sizing appropriate? Was the risk reasonable? If you made a sloppy decision that happened to work out, do not let the good outcome validate the sloppy process. Because next time, that sloppy process might produce a very different result.

As the chapter’s opening quote says: “Insanity is doing the same thing in the same way and expecting a different outcome.” I would add: it is also insanity to do a bad thing once, get a good outcome, and assume the bad thing is now a good strategy.

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Next: Recency Bias

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