Former Federal Reserve Chairman Alan Greenspan died Monday at 100, leaving behind a legacy defined by his cryptic economic pronouncements and one crystal-clear phrase: irrational exuberance. In a 1996 speech to the American Enterprise Institute, he questioned how to price software and services in an economy shifting from durable goods, highlighting the difficulty of valuing fast-changing technologies.

His warning preceded the dot-com bubble's peak by years, as companies like Webvan and Pets.com went public at inflated valuations before collapsing. Networking giant Nortel Networks fell from Canada's most valuable company to penny stock status. Yet survivors like Google and Amazon proved his point about selective success, with both now worth nearly $8 trillion combined.

In 1999 congressional testimony, Greenspan compared internet stock buying to lottery tickets, noting people overpay for remote chances at huge wins. Today's AI boom mirrors this dynamic, but with crucial differences. Companies like SpaceX and Anthropic carry massive valuations—Anthropic reached $965 billion post-money, while OpenAI hit $852 billion. These aren't small speculative plays but established giants priced for success.

The parallels to 1996 are striking: unprecedented valuations for money-losing companies in nascent industries, investor enthusiasm detached from fundamentals, and the same unanswered question of when exuberance becomes irrational. Greenspan's framework remains the sharpest lens for examining today's market dynamics.