Greater fool theory

The Greater fool theory is the expectation that an investor can profit from an overpriced asset by selling it to someone who will pay still more. In a controlled share-trading experiment, students said they knowingly bought shares at irrational prices because they believed they could collect dividends and pass the shares on to another buyer. The example shows how confidence in a future purchaser can sustain a bubble, while the book cautions that real bubbles are less transparent: participants may believe not only that they can sell at a higher price, but that the asset itself is worth far more than its underlying returns justify.

The wager on a later buyer

Economist Colin F. Camerer designed an experiment at the California Institute of Technology in which students traded shares in an imaginary company over fifteen five-minute periods. Each share paid a dividend of 24 cents at the end of each period. Because the experiment’s duration and payments were fixed, a share’s maximum value could be calculated in advance: $3.60 before trading began, declining by 24 cents after each period.

Despite that certainty, the share price quickly rose to $3.50 and remained there almost until the experiment ended. Students continued to trade at that price even as the shares’ remaining dividend value fell below $3, then below $2, and eventually below $1. The mismatch was unusually plain: unlike a real stock, the imaginary share’s future payouts were known, so paying more than the remaining dividends meant overpaying.

Asked why they had bought at prices they knew were too high, students explained that they had seen others trading at those prices and expected to collect a dividend or two before reselling at the same price to another buyer. Their reasoning depended on the belief that a later purchaser would take the loss. The theory’s name captures that succession: the present buyer is willing to be a fool only if someone else will be a greater one.

Why the experiment matters

The experiment stripped away several complications that might otherwise explain a bubble. Participants knew when trading would end, limiting the time available to resell their shares. They had the information needed to calculate the shares’ value, and they did not communicate except through buy and sell orders. No conversation was needed to encourage them or spread an explicit sales pitch; prices themselves supplied evidence of what other traders appeared willing to pay.

Even under these conditions, a bubble formed. The episode therefore illustrates the peril of dependent decision-making: traders looked to other people’s actions, and their willingness to buy helped preserve the high prices that others were observing. The prospect of selling on did not require each participant to deny the arithmetic. It required only a belief that another buyer would arrive before the opportunity disappeared.

From deliberate resale to genuine belief

The students openly described their strategy as looking for a greater fool, but the book distinguishes their candor from the psychology of real bubbles. People caught up in an actual boom may not recognize it as one. Some buyers may expect to resell at a higher price; others may sincerely believe that the asset’s value will continue to rise. These beliefs can coexist, making it harder to separate a resale wager from a judgment about fundamentals.

The book illustrates this ambiguity with buyers of Cisco shares when Cisco was the world’s most expensive stock. They may have believed that its price would keep climbing, but embedded in that expectation was also the possibility that Cisco really could be worth $500 billion. In a real bubble, therefore, the greater-fool logic need not appear as a conscious admission that the asset is overpriced. It may be entangled with an apparently substantive belief about what the company is worth.

The bubble’s changing appearance

A bubble can become less recognizable the longer it lasts. Its eventual endpoint is uncertain, and even in retrospect it may be difficult to say exactly when it began. During the Nasdaq boom, pundits predicted a collapse in 1998; an investor who had left the market then would have missed a 40 percent gain, while leaving before 1999 would have meant missing an 85 percent gain. Continuing rises can make the extraordinary seem like the ordinary, and an early warning can look mistaken for years before the danger becomes clear.

The book does not reduce bubbles to collective hysteria. Following others can be useful: if a group is generally intelligent, its members may help produce a stock price that is right. The danger emerges when everyone relies on the group’s judgment and no one contributes independent information to it. The greater-fool expectation is one expression of that dependence, but the broader problem is that a price sustained by people copying one another can stop reflecting fresh judgment about the asset. Like a beauty contest that can identify the prettiest contestant only if some judges actually consider who is prettiest, a market needs independent thought if collective judgment is to remain informative.