Twenty-five posts. That is what it took to retell this book. And honestly, when I started this series back on February 4th, I was not sure I would finish it. A post a day for almost a month is a lot. But here we are.
So after all the chapters, all the experiments, all the arguments back and forth, Burton and Shah finally ask the big question. Who wins? Is the market efficient or not? Time for a new theory entirely?
Can you grow a stock market bubble inside a classroom? Not a metaphor. An actual bubble where prices rise above what everyone in the room knows the thing is worth?
You know all those behavioral biases we talked about in earlier chapters? Loss aversion, status quo bias, overconfidence. The big question hanging over all of them is simple. Where do they come from? Are we born with them? Did we learn them from our parents and culture? Or is there something deeper going on inside our actual brains?
Try selling your house by tomorrow. Not in a month, not after listing it and staging it and waiting for offers. Tomorrow. For cash.
Stocks make more money than bonds. Everyone knows that. But here’s the thing. They make way more money than bonds. And when economists tried to explain why the gap is so big, they couldn’t. Not with their standard models. Not even close.
What if I told you that the day of the week affects your stock returns? Or that one specific month is consistently better than the other eleven? Sounds like astrology for finance people, right?
Every trader has said something like this at some point: “The stock has good fundamentals, it’s cheap, but the price action looks terrible. I’m going to wait.”
Benjamin Graham is probably the most famous contrarian investor who ever lived. Together with David Dodd, he invented what we now call value investing. The whole idea is simple. Buy stocks that other people don’t like. Stocks with low prices compared to their earnings or book value. Cheap stocks. Unpopular stocks.
In 1992 two economists published a paper that accidentally shook the foundations of modern finance. They did not mean to. They were actually trying to defend the system. But what they found in the data was so clear and so stubborn that it changed how everyone thought about stock prices.
You ever played the Madden NFL video game? For years, EA Sports put a top player on the cover. And then something funny kept happening. The cover athlete would have a terrible next season. Injuries, bad stats, team losses. Fans started calling it the Madden Curse. Some players actively tried to avoid being on the cover.
Every day you make decisions based on past data. What to eat for breakfast. How to approach your boss with a question. You look at what happened before and try to predict what will happen next.
People are sticky. Not physically. Mentally. We stick to whatever we already have, whatever is already happening, whatever is the default. And this stickiness costs investors real money every single day.
We all like to think we’re smart. If we didn’t think we were going to make money, we wouldn’t invest. But here’s a cold splash of water: 93% of American drivers think they’re “above average.” Mathematically, that’s impossible.
You know that feeling when you buy a stock right after seeing a scary headline, and then two weeks later you wonder what you were thinking? That’s a perception bias doing its work on your brain.
You know that feeling when you lose a $20 bill on the street? It ruins your whole afternoon. But finding $20 on the street? Nice, sure. You smile for maybe five minutes and forget about it.
Wandering around the average investor’s mind is like taking a tour of Wonderland with the White Rabbit. Most of what we think is true is actually false.
Economics has a favorite character. The Rational Man. He always knows what he wants. He always picks the best option. He never panics, never gets confused, never makes a dumb choice because he’s tired or emotional.
I’ve spent over 20 years in IT and a lot of time looking at charts and numbers. One thing I’ve learned is that the math is often the easy part. The hard part is the gray matter between your ears.
You ever watch financial news and hear someone say “the market broke through resistance” or “the market looks tired”? These phrases sound like the market is some living creature with feelings. And if you come from a science background, your first reaction is probably: what does that even mean?
Remember the dot-com bubble? Companies with zero profit, sometimes zero revenue, trading at insane valuations. Analysts invented new ways to justify the prices. “Forget earnings, count the eyeballs!” And for a while, it worked.
For decades, traditional finance people had a simple answer to the noise trader problem. Milton Friedman said it. Eugene Fama said it. Fischer Black said it. The answer was: irrational traders will lose their money to smart traders and disappear.
Economics has a rule that sounds so obvious it barely needs saying. If two things are identical, they should have the same price. If they don’t, someone will buy the cheap one and sell the expensive one until prices meet in the middle. Easy. Done. Move on.
Before behavioral finance became a real academic field, people already knew something was off with markets. Traders in the 1920s had their own rules. Value investors in the 1930s had theirs. And nobody was waiting for professors to tell them the market was irrational. They lived it every day.
Chapter 2 of Burton and Shah’s book is about the math behind stock prices. Don’t run away yet. I promise to keep it simple. The chapter introduces something called CAPM and the “market model.” These are the tools that traditional finance uses to describe how stock prices should behave. And if you want to understand why behavioral finance matters, you need to know what it’s arguing against.
Chapter 1 of Burton and Shah’s book gets right to the big idea. The Efficient Market Hypothesis. EMH for short. This is the theory that traditional finance is built on, and it is the thing behavioral finance tries to tear apart.
Let me tell you something that took me years to figure out. Traditional economics and finance are built on one really big assumption: that people are rational. And not just a little rational. Perfectly, mathematically, always-making-the-best-choice rational.
I’m starting something new here. Over the next 25 days, I’m going to retell the book Behavioral Finance: Understanding the Social, Cognitive, and Economic Debates by Edwin T. Burton and Sunit N. Shah.