Cisco's stock took 25 years to reclaim its year-2000 peak, despite the underlying business growing significantly. This serves as a stark reminder that even a successful, growing company can deliver zero returns for decades if an investor buys in at an extremely high, bubble-era valuation.

A true market bubble isn't defined by high valuations but by collective psychology. The most dangerous bubbles form when skepticism disappears and everyone believes prices will rise indefinitely. Constant debate about a bubble indicates the market hasn't reached that state of universal conviction.

Bubbles are created when assets like startup equity are valued astronomically, creating immense perceived wealth. However, this "wealth" is not money until it's sold. A crash occurs when events force mass liquidation, revealing a scarcity of actual money to buy the assets.

The dot-com era was not fueled by pure naivete. Many investors and professionals were fully aware that valuations were disconnected from reality. The prevailing strategy was to participate in the mania with the belief that they could sell to a "greater fool" before the inevitable bubble popped.

Cliff Asness differentiates two market manias: 2020 saw wider value spreads (pure valuation extremity). However, the dot-com bubble was uniquely dangerous because investors paid massive premiums for low-quality, "crap" companies—a toxic, multi-dimensional combination of risk factors.

Widespread public debate about whether a market is in a bubble is evidence that it is not. A true financial bubble requires capitulation, where nearly everyone believes the high valuations are justified and the skepticism disappears. As long as there are many vocal doubters, the market has not reached the euphoric peak that precedes a crash.

A market enters a bubble when its price, in real terms, exceeds its long-term trend by two standard deviations. Historically, this signals a period of further gains, but these "in-bubble" profits are almost always given back in the subsequent crash, making it a predictable trap.

Asnes employs a strict framework before using the word "bubble." He will only apply the label after exhaustively attempting—and failing—to construct a set of assumptions, however improbable, that could justify observed market prices. This separates mere overvaluation from true speculative mania disconnected from reality.

In a late-stage bubble, investor expectations are so high that even flawless financial results, like Nvidia's record-breaking revenue, fail to boost the stock price. This disconnect signals that market sentiment is saturated and fragile, responding more to narrative than fundamentals.