Judging an investment by its return is a psychological trap that confuses luck with skill and threatens long-term financial success.

The Illusion of the Result

You cannot evaluate an investment decision based on its outcome. This is a difficult concept for the human brain to grasp because we are hardwired with an "illusion of control" bias, leading us to overestimate our influence on external events. If you buy a speculative stock and double your money, you may feel like a genius, but you likely still made a bad decision. You simply had a good outcome. In an environment defined by uncertainty, the link between the quality of a choice and the quality of the result is often severed by luck.

To be a successful long-term investor, you must learn to look past the immediate scoreboard. When we recognize the difference between a bad decision and a bad outcome, we become better equipped to stick with a sensible strategy even when it isn't producing immediate rewards. Evaluating a decision must start at the moment the choice is made, based on the information available then, rather than through the distorted lens of hindsight.

The Logic of Risk Premiums

A sound investment decision is one where you know exactly what risk you are taking, why you are taking it, and what the expected outcome is. For most, this means capturing the "market risk premium"—the return in excess of risk-free assets that investors expect for participating in the uncertainty of capitalism. Since 1900, the global market has delivered a risk premium of roughly 4.2%, surviving world wars and the total collapse of markets in Russia and China. Betting on this long-term persistence is a rational decision, regardless of what happens in any single year.

However, even a rational decision can lead to a decade of disappointment. In the United States, stocks have trailed risk-free Treasury bills about 15% of the time over ten-year periods. This isn't a failure of the strategy; it is the nature of risk. We see this clearly in the divergent lives of retirees. Two individuals who worked for 30 years and retired only two years apart—one in 1973 and one in 1975—could end up with vastly different wealth levels despite making identical investment decisions. The difference was not their intelligence, but the sequence of market returns.

The Value Trap and the Necessity of Grit

The challenge of separating process from outcome is most evident in factor investing, such as the preference for value stocks over growth stocks. Historically, value stocks have outperformed growth by significant margins across global markets. Yet, for the past decade, U.S. value stocks have trailed growth significantly. Does this make the decision to tilt toward value a mistake? Not necessarily. If the decision was based on capturing an independent, risk-based premium, the strategy remains sound even if the recent outcome is poor.

The danger lies in abandoning the strategy right before it pays off. In March 2000, value stocks looked like a failed experiment, having trailed growth for the previous 20 years. Just one year later, after the dot-com bubble burst, the data flipped: value had beaten growth over the 5, 10, 15, and 20-year periods. To receive the expected premium, you had to endure two decades of underperformance and have the fortitude to hang on for that final, transformative year. This is why consistency often matters more than brilliance.

Diversification as Luck Insurance

While we cannot eliminate uncertainty, we can use diversification to reduce the role of luck. Diversification should extend beyond simple geography. While U.S. stocks struggled during the "lost decade" of 1999 to 2009, Canadian stocks and U.S. small-cap value stocks provided substantial positive returns. By spreading bets across different regions and risk factors—such as size, value, and profitability—investors can smooth out the ride.

The math of factor diversification is compelling. Looking at rolling ten-year periods since 1963, one of the four major risk premiums was negative roughly 50% of the time. However, the instances where three out of four premiums were negative simultaneously occurred in only one out of 547 periods. By diversifying across these uncorrelated factors, you significantly lower the probability of a catastrophic outcome, allowing your long-term process the time it needs to work.

The Bayesian Mindset

To maintain this discipline, investors should adopt "Bayesian thinking." This involves starting with a strong "prior"—a belief based on decades of empirical evidence—and requiring an overwhelming weight of new evidence to change that belief. Most investors fall victim to the availability heuristic, where they give too much weight to recent events, like a few years of market volatility or a hot tech trend. They treat a short-term bad outcome as proof of a bad decision.

Ultimately, an investment decision should be judged only on the quality of the process used to make it. If you have a sound reason for taking a specific risk to achieve a specific goal, you must be prepared to stick with that strategy for an investment lifetime. It feels counterintuitive to "blindly" follow a plan, but in a world of noise and luck, a steadfast commitment to a proven process is the only reliable path to success.