The Final Act of the Superbubble: Jeremy Grantham on Market Irrationality Phases and Bear Market Rally Traps

In an investment career, truly significant market events are few, and "superbubbles" are among the most decisive. Jeremy Grantham points out that these events differ from ordinary bull-bear transitions; they possess unique common characteristics and are often accompanied by dramatic phase changes in investor behavior. The key to understanding this concept lies in identifying extreme valuation states that deviate more than 2.5 standard deviations from the trend, rather than merely focusing on daily market fluctuations.

Grantham divides the bursting process of a superbubble into four stages: first, bubble formation; second, the initial correction caused by flaws in the economic or political environment; third, the highly deceptive "bear market rally"; and finally, the ultimate decline triggered by deteriorating fundamentals. The bear market rally occurs after the initial devaluation but before a clear economic recession. Historical data shows that such rallies typically recover more than half of the initial drop, luring less vigilant investors back into the market, after which the market turns downward with even greater momentum.

Taking the cases of 1929, 1973, and 2000 as examples, the bear market rallies during these periods were extremely fast and large in magnitude. For instance, within two months after the burst of the tech bubble in 2000, the Nasdaq recovered 60% of its initial losses. The psychological mechanism behind this phenomenon is the anchoring effect: investors see stock prices fall significantly from their highs and mistakenly assume they have become "cheap," thereby ignoring the fact that valuations remain far above long-term averages. In contrast, new highs in normal bull markets are often accompanied by hesitation and slow progress due to the lack of historical price references.

For today's readers, the core question is how to distinguish between normal market corrections and the prelude to a superbubble burst. Grantham emphasizes that when the market is in a period of extreme optimistic irrationality (which accounts for approximately 12% of the time), traditional risk management strategies may fail. At such times, institutional managers often tend to follow the crowd and become "permanent bulls," as this is the best choice for career safety. However, for independent investors, identifying this collective behavioral phase change and being wary of the subsequent rapid rally is key to avoiding severe losses in the late stages of the bubble.