More Than You Know

In a 2012 study, researchers analyzed over 1.6 million surgical procedures performed by more than 2,000 surgeons. The data revealed a startling pattern: patient mortality rates were significantly higher for procedures performed late on a Friday afternoon compared to those done on a Monday morning. The surgeons were the same, the hospitals were the same, and the procedures were the same. The only variable that changed was the surgeon's accumulated fatigue and dwindling mental resources by the end of a long week. This is not an isolated phenomenon. A separate analysis of over 90,000 judicial rulings found that judges were dramatically more likely to grant parole at the beginning of the day or right after a food break. As the hours wore on, the percentage of favorable rulings dropped steadily, approaching zero just before the next break. Again, the facts of the cases didn't change; the decision-maker's cognitive state did.

These patterns reveal a fundamental, often invisible, force at play in high-stakes decisions, from the operating room to the courtroom to the trading floor. It's a force that fascinated Michael Mauboussin, a seasoned investment strategist and adjunct professor at Columbia Business School. For decades, he observed brilliant, highly trained professionals in finance make baffling errors because their thinking was flawed. He saw that success was about knowing how your own mind works, how crowds behave, and how to borrow proven models from fields as diverse as biology, physics, and psychology. He wrote More Than You Know to create a latticework of these powerful mental models, offering a multidisciplinary toolkit for anyone who has to make complex decisions under conditions of uncertainty.

Module 1: The Process is King

We are obsessed with outcomes. Did we win the deal? Did the stock go up? Did the product launch succeed? Mauboussin argues this focus is a trap. In a world governed by probability, a good process can lead to a bad outcome. And a bad process can get lucky. The key to long-term success is building and sticking to a sound decision-making process.

Think of a casino. The house doesn't win every hand. In fact, it loses quite often. But it has a process with a slight statistical edge. Over thousands of hands, that edge guarantees a profit. You must build a process with a positive long-term edge, then execute it relentlessly. This is the "Be the House" principle. A professional gambler doesn't bet big on a whim. They wait for the rare moments when the odds are in their favor. Then they act decisively.

Here's how this applies. Mauboussin tells the story of a blackjack player who hits on seventeen. He gets a four and wins the hand. The dealer says, "Nice hit." But it was a terrible decision. The process was flawed, even though the outcome was good. In investing, this happens all the time. Someone buys a speculative stock without research. It triples. They confuse their luck with skill. This reinforces a bad process, which eventually leads to ruin.

So, how do you build a good process? First, distinguish between fundamentals and expectations. A great company is not necessarily a great investment. The market price already reflects a set of expectations about that company's future. The real opportunity lies in finding a "variant perception." This is a well-founded view that differs from the market consensus. You need to ask: what is priced in? And what do I know that the market is missing? Steven Crist, a famous horse-racing handicapper, put it perfectly. The question is which horse has odds that are mispriced relative to its actual chance of winning.

Module 2: The Psychology of Dumb Money

Our brains are not wired for investing. They are wired for survival on the savanna. This wiring creates systematic glitches in our decision-making. These glitches, or cognitive biases, are the source of most investment errors. Understanding them is like having a superpower.

One of the most powerful biases is loss aversion. Research from Daniel Kahneman and Amos Tversky shows that we feel the pain of a loss about two and a half times more than the pleasure of an equivalent gain. This leads to irrational behavior. Investors sell their winners too early to lock in a gain and hold their losers too long to avoid realizing a loss. This is the exact opposite of what you should do.

And here's the thing. This bias is made worse by "myopic loss aversion." The "myopia" comes from checking your portfolio too often. If you check daily, you see volatility. You see losses. And because of loss aversion, it feels terrible. This emotional pain pushes you to make short-term, reactive decisions. But if you only evaluated your portfolio once a decade, the short-term noise would disappear. You would only see the long-term trend. The lesson? Lengthen your time horizon to neutralize your brain's flawed emotional wiring. A low portfolio turnover is a psychological defense mechanism.

Another critical bias is the "hot hand" fallacy. We are pattern-seeking machines. We see streaks everywhere. A basketball player makes a few shots in a row, and we think he's "hot." A fund manager beats the market for three years, and we assume they have a special skill. But in most random processes, streaks are statistically normal. A coin flip will produce streaks of heads. It doesn't mean the coin has a "hot side." The mistake is confusing skill and luck. Yes, skill exists. But long streaks of success are far rarer than we think. They require both skill and an extraordinary amount of luck. Bill Miller’s 15-year streak of beating the S&P 500 had odds of one in 2.3 million. Attributing that purely to skill is a mistake.