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There is a particular kind of pain reserved for the rational investor during a bull market. It is not the pain of losing money. It is the pain of watching everyone else make money doing things you know are stupid.
You have done the reading. You understand valuations. You can spot a bubble forming the way a surgeon spots a fracture on an X-ray. And none of it helps you. In fact, it actively hurts you.
Welcome to the only arena where knowledge is a handicap and ignorance prints money.
This is not just an observation. It is a problem with deep roots in game theory and microeconomics, and it explains why the smartest people in the room are often the last to get rich in a rising market.
The Coordination Problem Nobody Talks About
A bull market is not really about stocks going up. It is about people agreeing, mostly without talking to each other, to keep buying. This is a coordination game, and coordination games do not reward the person with the best information. They reward the person who best predicts what everyone else will do.
John Maynard Keynes described this decades ago with his beauty contest analogy. You are not picking the prettiest face. You are picking the face you think everyone else will pick. The moment you start analyzing bone structure and symmetry, you have already lost. The game is not about truth. The game is about consensus.
Rational investors misunderstand this at a fundamental level. They think the market is an information processing machine. It is, sometimes. But in a bull market, it is a voting machine, and the votes are driven by momentum, narrative, and the deeply human fear of missing out. Analyzing fundamentals during a momentum driven rally is like bringing a dictionary to a shouting match. You are technically better equipped and completely outgunned.
The Prisoner Who Refuses to Defect
Game theory gives us the Prisoner’s Dilemma, and the bull market version is brutal.
Imagine two investors. Both know that a stock is overvalued. If both sell, the price corrects and they preserve their capital. If both hold, the bubble keeps inflating and they both profit on paper. But if one sells while the other holds, the seller locks in modest gains while the holder rides the wave higher.
The rational move, strictly speaking, is to sell. But rationality assumes the other player is also rational. In a bull market, they are not. They are holding, buying more, and posting gains on social media. The rational investor who sells is not wrong. They are just early. And in finance, early and wrong feel identical.
This is the tragedy. Game theory tells us that in a one shot game, defecting (selling) is optimal. But a bull market is not a one shot game. It is an iterated game with an unknown endpoint. Every day the market goes up, the rational seller pays a psychological cost. Every day, the irrational holder collects a psychological reward. Over months, this asymmetry grinds down even the most disciplined mind.
Bounded Rationality and the Humility Problem
Herbert Simon, the Nobel laureate, gave us the concept of bounded rationality. The idea is simple but devastating: humans cannot process all available information, so they use shortcuts. They satisfice. They pick the option that is good enough rather than optimal.
Here is where it gets interesting. In a bull market, bounded rationality is not a bug. It is a feature. The investor who does not overthink, who buys the dip without modeling twelve scenarios, who follows the trend without questioning its sustainability, is operating within their cognitive limits and profiting because of it.
The hyper rational investor, meanwhile, is drowning in information. They see the debt levels. They see the margin calls waiting to happen. They see the historical parallels to previous bubbles. And all of this information, every single byte of it, tells them to be cautious. So they sit on the sideline with their analysis and their accuracy and brokerage account that is flat.
Simon would appreciate the irony. The person with less information is making more money precisely because they have less information to paralyze them.
The Asymmetric Payoff Structure
Microeconomics teaches us about asymmetric payoffs, and bull markets are a masterclass.
If you are rational and right, you avoid losses that have not happened yet. Your reward is the absence of pain. Nobody throws a parade for the person who did not lose money. If you are rational and wrong (meaning the bull market continues longer than you expected), you miss gains. Your punishment is visible, measurable, and discussed at every dinner party.
Now flip it. If you are irrational and right, meaning you bought overvalued assets and they kept going up, you are a genius. If you are irrational and wrong, meaning the bubble pops, you are in good company. Everyone lost. It is a systemic event. The government might even bail you out.
Read that payoff matrix again. Being irrational has a higher expected social and financial return in a bull market than being rational. This is not a flaw in the argument. This is a flaw in the market structure, and it is one that game theory predicted decades ago. The incentive to join the crowd always outweighs the incentive to stand apart, right up until the moment it does not.
The Network Effect of Delusion
There is a concept in economics called network effects. A product becomes more valuable as more people use it. Telephones, social media, the English language. The more participants, the more value each participant gets.
Bull markets have network effects. Every new buyer pushes prices higher, which validates the thesis of existing holders, which attracts new buyers. The network grows. The narrative strengthens. And rationality becomes an increasingly lonely position.
When most investors are rational, the rational investor has an edge. But when most investors are momentum chasers, the rational investor is the odd one out. Their strategy, which is objectively superior in isolation, becomes inferior in context. The environment selects against them.
This is uncomfortable to admit, but strategy quality is not absolute. It is relative to the population you are competing against.
The Information Cascade
In microeconomics, an information cascade occurs when people abandon their private information and follow the crowd. It is rational, in a twisted way. If you see a hundred people walking into a restaurant, you might ignore your own bad review and follow them in. They must know something you do not.
Except they do not. They are all following the person ahead of them, who is following the person ahead of them, and the first person just liked the sign out front. Nobody has private information. Everyone has social proof.
Bull markets are information cascades on steroids. Each new all time high is a signal, and not a signal about the underlying value of the assets. It is a signal about the behavior of other participants. And the rational investor who says “this signal is meaningless” is technically correct and practically irrelevant.
The cascade does not care about your DCF model.
So What Do You Actually Do?
If you have read this far, you might expect me to say “so just be irrational.” I will not, because the bull market eventually ends, and when it does, the irrational investor gives back everything and more. The wreckage of 2000, 2008, and 2022 was populated almost entirely by people who thought rationality was optional.
The real lesson from game theory is not that rationality is useless. It is that pure rationality, applied without regard for the game you are actually playing, is self defeating. The best poker players do not always play the mathematically optimal hand. They play the hand that exploits the tendencies of the table.
In a bull market, the table is full of momentum players. The rational approach is not to ignore this. It is to incorporate it. Acknowledge that prices can remain irrational longer than you can remain solvent, as the old saying goes. Participate, but with position sizing that reflects the elevated risk. Hold, but with a clear framework for when the game changes.
The most sophisticated application of game theory is not stubbornly playing your dominant strategy while the game shifts around you. It is recognizing which game is being played and adapting your strategy accordingly, without abandoning your principles entirely.
The Final Irony
The deepest irony in all of this is temporal. The rational investor is almost always vindicated. Bubbles pop. Valuations revert. Fundamentals reassert themselves. But vindication and profit are not the same thing.
You can be right about the destination and still lose money on the journey. You can identify every crack in the foundation and still watch the building climb higher for years. The market does not compensate you for being correct. It compensates you for being correct at the right time.
And timing, as any game theorist will tell you, is not a function of analysis. It is a function of coordination. You need to be right at the same time enough other people are right to move the price in your direction.
Until then, you sit with your spreadsheets and your skepticism, watching the parade go by, knowing exactly how it ends but not when.
That is the tax on rationality. You pay it in missed gains, in social isolation, in the quiet agony of watching the wrong people make the right returns. And the receipt, when it finally comes, says: “You were right. Congratulations. Everyone else got rich first.”
