FOMO, herd behavior and bubbles

FOMO, or fear of missing out, is the urge to buy something because it has been rising and others appear to be profiting. Herd behavior is the broader tendency to follow what the crowd is doing instead of your own analysis. Together they explain why many investors buy near peaks and sell near lows, and why asset bubbles recur across centuries.

Why people follow the crowd

Following others is not always irrational. Several forces make it hard to resist:

• Social proof. If many people are buying, it is natural to assume they know something.
• Information cascades. Each buyer partly relies on the choices of earlier buyers, so a small initial signal can snowball with no one checking the underlying facts.
• Regret. Missing a big gain feels worse than a loss shared with everyone else.
• Career and reputation risk. Professionals fear underperforming while a trend continues, even if they think it is overpriced.
• Constant visibility. Social media and news feeds show other people's wins, while the losses stay quiet.

How bubbles form

A bubble is a period when prices rise far above any reasonable estimate of underlying value, supported mainly by the expectation that prices will keep rising. A stylized model of the cycle, often associated with economist Hyman Minsky and later developed by Charles Kindleberger, has five stages:

1. Displacement. A new development, such as a technology or a change in policy, creates real excitement.
2. Boom. Prices rise, and attention grows.
3. Euphoria. Caution fades, justifications shift from earnings to "this time is different," and new buyers arrive mainly because prices are rising.
4. Profit-taking. Informed or cautious holders begin to sell.
5. Panic. Prices fall quickly, and herd behavior reverses into forced and fearful selling.

History offers many examples. The South Sea Company bubble in Britain peaked in 1720. The Nasdaq Composite reached a peak in March 2000 during the dot-com boom and then fell roughly 78% by October 2002, and it took well over a decade to regain that peak. US housing prices rose rapidly in the mid-2000s before falling. In early 2021, a handful of heavily shorted stocks rose and fell sharply in episodes driven by social-media coordination. The details differ, but the pattern of excitement, extrapolation, and reversal is recognizable.

Honest limits

Bubbles are easier to see afterward than in real time. A rising price is not proof of a bubble, and a stock can look expensive for years before falling or never fall. Selling early on the suspicion of a bubble can cost as much as buying late. The practical aim is not to call tops, but to avoid decisions that depend on the crowd and to avoid sizes that a reversal would make unbearable.

Example (illustrative numbers)

A stock rises from $50 to $100 in three months. News coverage is everywhere, and friends mention it. You buy at $100 because you do not want to miss more. Over the next quarter it falls back to $60, a 40% loss from your entry.

The better question before buying at $100 is what the price implies. Working backward from the price to the growth and margins required, as in a reverse DCF, may show that the market already expects far more than the company has ever delivered. That does not mean the price must fall, but it tells you what has to go right for you to earn a reasonable return. If you cannot explain why $100 is reasonable and $50 was not, the decision rests on the crowd.

Warning signs (rules of thumb)

None of these is a signal on its own, and none predicts timing:

• Valuations far above the company's own history and its peers, without matching growth or profitability.
• Explanations that move away from earnings and cash flow toward stories and new metrics.
• Heavy participation by first-time investors and heavy use of borrowing.
• The main argument for buying is that the price is rising.
• Reasoning that dismisses any skeptic as not understanding.

The mirror image: panic

Herd behavior also works on the way down. In a sharp decline, selling can feel urgent and seem like the only sensible choice. Investors who sell near lows lock in losses and often miss the early part of recoveries. Understanding that a bear market is a regular feature of investing makes it easier to hold a plan.

Defenses

• Use a written checklist before any purchase, so excitement cannot skip a step. See a practical checklist before you buy.
• Anchor on value, not momentum. Estimate what the business is worth, as a range, and compare the price with it. See fair value is a range.
• Limit position size in anything you buy for excitement.
• Wait a day or two before acting on an impulse purchase.
• Reduce the feed. Following fewer hot-stock conversations lowers the pressure.
• Know your bias. See behavioral biases.

Where to see it on StocksXray

The overvalued list shows stocks labeled Overvalued by the fair value models, and the new 52-week high scanner shows stocks making new highs. Neither is a prediction: a stock can stay above fair value for a long time, and rising prices alone do not mean overvaluation. Typical model error is around 40%, so the labels are a prompt for questions rather than conclusions.

Key takeaways

• FOMO and herding are strong, natural pulls that lead to late buying and panic selling.
• Bubbles follow a recognizable pattern, but are hard to time in advance.
• Ask what a price implies before buying something that has run up.
• A written process, sensible position sizes, and a value anchor are the practical defenses.
• Missing one opportunity costs less than a large loss in a crowded trade.