📖Jeremy Grantham
Mean Reversion
High valuations predict low future returns.
Asset class returns revert to the mean. High valuations predict low future returns; low valuations predict high returns.
🏠 Everyday Analogy
📖 Core Interpretation
In Mean Reversion, Jeremy Grantham focuses on the gap between price and value. Returns come from paying less than what a business is worth, not from guessing short-term market moves.
💎 Key Insight：Mean reversion is the most reliable force in markets. When asset prices deviate far from historical averages, they eventually return. High P/E ratios, CAPE, or price-to-sales predict below-average returns over the next 7-10 years with remarkable consistency. Grantham's firm has proven this across decades and asset classes. Valuation is destiny over the long term.
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❓ Why It Matters
Ignoring valuation turns even good companies into poor investments. Overpaying compresses future returns and leaves little margin when assumptions are wrong.
🎯 How to Practice
Estimate intrinsic value with conservative assumptions, set clear buy ranges, and act only when price offers a meaningful discount with acceptable downside.
🎙️ Master's Voice
The market can remain irrational longer than you can remain solvent.
Grantham warns that being right too early is the same as being wrong. Bubbles can last longer than expected.
⚔️ Practical Guide
✅ Decision Checklist
- Can I survive being early?
- How long can irrationality last?
- Am I prepared to wait?
📋 Action Steps
- Prepare for long irrationality
- Maintain solvency
- Be patient
🚨 Warning Signs
- Insufficient patience
- Risking solvency
- Being too early
⚠️ Common Pitfalls
Confusing a low price with true cheapness
Using one metric without business context
Overly optimistic assumptions that erase margin of safety
📚 Case Studies
1
Dot-Com Bubble Mean Reversion (2000)
Grantham warned that tech stocks were absurdly overvalued versus historical norms and trimmed GMO’s exposure before the crash.
✨ Outcome：When the bubble burst, GMO portfolios fell less than the market and later redeployed into cheaper equities as valuations normalized.
2
U.S. Housing and Credit Bubble (2007)
Grantham highlighted extreme overvaluation in U.S. housing and risk assets, cutting exposure to equities and credit pre-crisis.
✨ Outcome：GMO avoided the worst of the 2008 collapse and then added risk as spreads and equity valuations reverted toward historical averages.
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