The greater fool theory: The root cause of market bubbles?

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Looking for a fool to take the other side of your riskiest trades?

© Photocreo Bednarek/stock.adobe.com; Photo illustration Encyclopædia Britannica, Inc.

Suppose a stock that’s been hyped on social media goes viral, infecting the social trading space with a severe case of FOMO (fear of missing out). Now, everyone’s talking about it, and soon people begin buying in droves, clogging up the digital order flow space with a frenzied folly of bids.

The stock is already up over 100% from its lows, and by your own estimates, that’s way overvalued—disconnected from its fundamental worth. Yet its price keeps advancing. Do you pass it up, wait for the price to pull back a bit, or do you pull the trigger and buy some shares?

The overblown narrative lifting the stock has proven compelling enough to take prices this far, so why not aim higher? And surely, somewhere in the stratosphere of lofty values, there’s likely to be someone who’s willing to pay an even more exorbitant price down the road, right?

That’s the basis of the greater fool theory. As a trading strategy, it’s an extreme (if not cynical, and most definitely risky) version of a key component of technical analysis—trading on momentum. But as any veteran momentum trader will tell you, when a momentum trade turns into a “bubble trade,” it can go from lucrative to dangerous at a moment’s notice.

Betting on a “greater fool” outcome seems risky, more like gambling than trading. After all, it’s about investing in a bubbling asset or assets in a bubbling market. So, why not just avoid it? Well, it’s not that clear-cut or simple. Not all bubbles are the same. As we’ll see, some are hard to identify and difficult to avoid.

A speculative bubble is when the price of an asset rises above its fundamental value due to excessive hype driving ever-higher prices, which generates more hype in a feedback loop. In a speculative bubble scenario, investors are willing to pay higher prices for an asset whose real value may be much less. This can apply to single assets or to a group of assets within a broader industry, sector, or market.

So, what drives excessive speculation? It depends on the type of bubble.

More often than not, short-term bubbles are driven by some form of hype. It might be a news report, a celebrity announcement, a social media post gone viral, or any kind of communication that can persuade a large number of people to buy an asset.

When assets experience this type of bubble, their prices are bid up rapidly—fueled not by fundamental value, but rather by narrative.

For example, in 2021, shares of GameStop (GME), AMC (AMC), and other so-called meme stocks jumped orders of magnitude over a few days following viral social media posts that prompted retail investors to swarm shares with ever-increasing bids and buys. For the most part, these stocks came back to earth in short order (see figure 1).

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Figure 1: FOOLING AROUND WITH MEME STOCKS? GameStop was one of the first “meme stocks” that took off in early 2021.

Image source: Barchart.com. Annotations by Encyclopædia Britannica, Inc.

Long-term bubbles are trickier to detect, as they form gradually and move slowly. These bubbles can last for years, especially if they’re supported by low interest rates (low borrowing costs), which can increase the demand for riskier assets. Typically, this helps boost jobs, wages, wealth perception, and consumer demand. When broad demand outpaces supply, prices tend to inflate, and this includes financial assets.

In a booming economy on the verge of “overheating,” it’s often difficult to tell whether asset prices (like stocks and real estate) are rising thanks to increased value or just plain speculative demand, what former Fed chair Alan Greenspan called “irrational exuberance.”

As an investor (and not a florist), how do you evaluate the financial fundamentals of a tulip bulb? It might sound like an odd question, because tulips aren’t traditional financial instruments. They don’t have the durability common to most collectibles, and they’re not consumable or functional like commodities such as food and gasoline. Yet, they’re infamous for being the focal point of Tulip Mania, one of the most outrageous speculative bubbles in history.

More recently, the cryptocurrency space has shown a similar phenomenon, this time with digital financial assets. Unlike tulips, cryptocurrencies were designed either to provide alternative monetary value or to facilitate financial processes. The problem is that there’s no standardized way to measure crypto fundamentals. The industry is still in relative infancy. So it’s almost like having no fundamentals at all, because there’s no surefire way to measure them.

Yet, mass crypto speculation caught on like wildfire, bubbling and bursting in 2017 and 2021 before rebounding again during the mid-2020s (see figure 2).

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Figure 2: FOOL ME THRICE? After soaring to new heights, Bitcoin lost more than 80% of its value—twice—only to reach a new high in 2025, followed by yet another steep sell-off.

Source: StockCharts.com; annotations by Encyclopædia Britannica, Inc.

Should you avoid overvalued assets, or might you consider betting on a greater fool to help you cash in?

Exploiting a short-term bubble can be ultra-risky. Short-term bubbles can burst in a matter of days, hours, or even minutes. This type of speculation is more of a trade than an investment. Whether you can pull it off really depends on your trading experience, whether you’re able to “babysit” your trades each day, and—let’s be honest—whether you’re feeling lucky.

In other words, you should either be a trading pro, or you should be playing with money you can afford to lose.

But if you’re dealing with a long-term bubble—one that could go on for years—then you face a dilemma. You can either risk time in the market (investing despite a potential bubble) or timing the market (waiting for it to burst, if it is indeed a bubble).

This is where your portfolio management principles and skills come into play. If you’re investing for the long term and using sound risk management principles, then the greater fool theory may not be so relevant to your far-horizon strategy or goals.

It seems there are always greater fools in the market willing to pay high prices for assets on the verge of correction or collapse. The problem is that it’s hard to know how many are out there, whether their numbers are dwindling, and whether the few that are left are wising up.

Sometimes the “greater fool” is a matter of perspective that has more to do with your approach to trading versus investing. If you’re investing with the assumption that a greater fool might be out there, just remember that it could be you.