Introduction to Behavioral Biases: Why Your Brain Sabotages Your Portfolio

Chapter 3 of Pompian’s book is short but important. It is the setup chapter. Before getting into 20 specific biases over the next 20 chapters, he wants you to understand what biases are, why they matter, and how they break down into categories.

The chapter opens with a quote from a Spanish philosopher: “What we believe to be the motives of our conduct are usually but the pretexts for it.” That is a polite way of saying we lie to ourselves about why we do things. And when it comes to money, we lie to ourselves constantly.

The Toothpaste Problem

Here’s the thing about decision-making. When problems are simple, we handle them fine. But when things get complex and require real cognitive effort, we take shortcuts. Pompian uses a great everyday example: walk down the toothpaste aisle at a supermarket. There are way too many choices. How do you pick? Most people just grab what they grabbed last time. And that is one of the easier decisions we make.

Now think about financial decisions. Which stocks to buy. How to allocate your retirement. Whether to sell or hold during a crash. These are genuinely hard problems with massive amounts of information to process. And instead of systematically analyzing all the data and options, most people simplify. They cut down the choices to a manageable number, use some rough rules of thumb, and pick something that feels “good enough.”

This is not necessarily bad. We would be paralyzed if we tried to make every decision perfectly. But here’s the problem: these shortcuts create systematic errors. Not random errors that cancel each other out over time, but predictable, repeatable mistakes that push us in the wrong direction. Those systematic errors are what we call biases.

Two Flavors of Wrong

Pompian divides all biases into two big categories: cognitive and emotional. This distinction matters a lot because it determines how you can deal with them.

Cognitive biases come from faulty reasoning. Your brain makes a statistical error, processes information wrong, or remembers things incorrectly. Think of these as software bugs. The good news is that cognitive biases can often be fixed with better information and education. If someone explains to you that your reasoning is flawed and shows you the data, you have a decent chance of changing your behavior.

Emotional biases come from feelings, impulses, and intuition. These are harder to fix because they are not based on logic in the first place. You cannot educate someone out of fear or greed. You can point out the bias, but the person might get defensive rather than receptive. With emotional biases, the best strategy is often to just acknowledge them and work around them instead of trying to eliminate them.

I think about this in terms of my own experience. When I was teaching at university, I could correct a student’s wrong calculation by showing them the right formula. That is fixing a cognitive error. But when a student was anxious about an exam and their anxiety made them perform poorly, showing them a formula did not help at all. You had to address the anxiety itself. Same thing with investing.

Cognitive Biases: Two Sub-Types

Pompian breaks cognitive biases down further into two groups.

Belief perseverance biases. These are about clinging to what you already believe, even when new evidence contradicts it. This is closely tied to cognitive dissonance, which is the uncomfortable feeling you get when reality clashes with your beliefs. To avoid that discomfort, people do three things:

• Selective exposure: they only seek out information that confirms what they already think
• Selective perception: they ignore or twist information that conflicts with their beliefs
• Selective retention: they remember only the stuff that supports their existing view

Sound familiar? Think about how people handle their investment picks. You buy a stock, and then you only read positive articles about it. You dismiss the negative ones as “FUD.” You remember the times your picks went up and forget the losses. We all do this.

The six belief perseverance biases covered in the book are: cognitive dissonance, conservatism, confirmation, representativeness, illusion of control, and hindsight.

Information processing biases. These are about how you handle and use information in the moment. Not so much about holding onto wrong beliefs, but about the actual processing errors you make when analyzing data. The seven processing biases are: anchoring and adjustment, mental accounting, framing, availability, self-attribution, outcome bias, and recency bias.

The book covers 13 cognitive biases total. Each one gets its own chapter with diagnostic questions and case studies.

Emotional Biases: The Harder Problem

Emotional biases are a different beast. An emotion is a mental state that arises on its own, not through conscious effort. You do not choose to feel fear when the market drops 10% in a day. It just happens. And even if you know the fear is irrational, you often cannot stop it.

The six emotional biases in the book are: loss aversion, overconfidence, self-control, status quo, endowment, and regret aversion.

Here’s what I found most interesting about Pompian’s take on emotional biases. He says that when you identify an emotional bias in someone (or yourself), pointing it out directly is likely to backfire. The person gets defensive. Instead, you have to be clever about it. Change the questions you ask. Change the decision-making process. Guide people toward better decisions without telling them they are being irrational.

This is basically what Thaler and Sunstein were talking about with “nudging” in the previous chapter. You do not fight human nature. You design systems that work with it.

Why This All Matters Practically

Pompian shares something from his personal experience that stuck with me. He has been in wealth management for over 20 years, through the crashes of 1987, 1998, 2001, and 2008. He says that simply identifying a bias at the right moment has saved many of his clients from financial disaster.

During market meltdowns, his main job was talking clients “down from the ledge” and stopping them from selling everything at the worst possible time. That is loss aversion in action. People feel the pain of losses so intensely that they want to do anything to make it stop, even if selling at the bottom locks in massive losses.

He also gives the example of clients who have a gambling instinct. Instead of fighting it, he carves out a small percentage of their portfolio for risky bets and keeps the rest in a solid, diversified plan. That is adapting to an emotional bias rather than trying to eliminate it.

This practical approach is what makes the book valuable. Pompian is not just describing biases in a theoretical way. He is saying: here is how you deal with them in real life, with real money, with real people who have real emotions.

The Framework Going Forward

So the structure for the next 20 chapters is set. Each bias will be named, categorized as cognitive or emotional, described in general and technical terms, illustrated with a case study, and followed by diagnostic questions you can use to test yourself (or your clients) for that bias.

Pompian makes an important disclaimer: the study of behavioral finance is still young. There is no grand unified theory of investor behavior yet. The field is a collection of evidence that humans are bad at making financial decisions in predictable ways. That is honest and I appreciate it. Too many books promise a complete system. This one just says: here are the patterns, here is how to spot them, here is what to do about them.

One last thing I want to highlight. Pompian says the cognitive vs. emotional distinction is not always clean. Some biases have elements of both. And some biases relate to each other. Real human psychology is messy. But having even an imperfect framework is better than having no framework at all.

We are now ready for Part Two, where we get into the specific biases one by one. The first one up is cognitive dissonance, which is the foundation for many of the belief perseverance biases. I am looking forward to it because cognitive dissonance is something I see everywhere, not just in investing.

Previous: History of Behavioral Finance

Next: Cognitive Dissonance Bias

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