Bubbles, Explained: How They Form, Why They Are Obvious Only Afterwards

Foundations

A bubble is a sustained rise in prices far beyond what the underlying cash flows can justify, powered by the belief that someone will always pay more. The word is thrown at every rally; genuine bubbles are rarer, stranger, and follow a script old enough that the 1630s tulip episode still reads like a modern case study.

The anatomy: from story to mania

Bubbles begin with a genuine story: railways, electricity, the internet, arguably any transformative technology. Early investors profit, which attracts imitators; credit expands to fund the buying; prices rising becomes the evidence that prices will rise. In the mania phase, valuation arguments are replaced by narrative ones (“this time is different”, “old metrics do not apply”), scepticism becomes professionally dangerous, and supply responds: floods of new issuance, new funds, new products manufactured to meet the demand.

Why they are only obvious afterwards

The uncomfortable truth: transformative technologies DO sometimes justify extraordinary valuations, and the loudest bubble-callers have been wrong for years at a time. The internet was real even though 2000 was a bubble; the railways changed the world even as railway shares ruined a generation. The analytical task is not shouting “bubble” but separating the technology’s trajectory from the price’s: infrastructure overbuilt in a mania often powers the next era, profitably, for whoever buys it from the receivers.

The tells, and the ending

Recurring warning signs: purchases financed with leverage, valuations sustained only by fresh inflows, supply ramping to meet demand, and insiders selling to the public (the IPO flood). The end usually needs no dramatic trigger: prices stop rising, which breaks the only reason many holders owned the asset, and the reflexive machine runs in reverse, amplified by the margin calls of everyone who borrowed on the way up. Our AI coverage returns to this checklist constantly, on both sides of the argument.