📖John Bogle
Learn from Past Sells
Post-mortem every sell decision to improve.
After every sell, review the outcome. Did you sell too early, too late, or at the right time? Post-mortems on sell decisions improve future judgment.
🏠 Everyday Analogy
📖 Core Interpretation
John Bogle sees markets as cyclical rather than linear. Understanding cycle position improves risk-taking decisions more than trying to call exact tops and bottoms.
💎 Key Insight：Reviewing sell decisions sharpens future timing.
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❓ Why It Matters
Ignoring cycles repeats the same mistakes: excessive optimism at peaks and excessive pessimism near troughs. Context matters for position sizing.
🎯 How to Practice
Monitor credit, valuation, earnings, and sentiment signals; reduce aggressiveness in euphoric phases and preserve flexibility in fearful phases.
⚠️ Common Pitfalls
Treating short rebounds as full cycle turns
Extrapolating peak conditions indefinitely
Becoming maximally defensive near valuation troughs
📚 Case Studies
1
Target-Date Funds in the 2008 Financial Crisis (2008)
In 2008, the S&P 500 fell about 37%, but investors in target-date funds with higher bond allocations (near-retirees in 2010 funds) typically lost far less than younger investors in stock‑heavy 2050 funds. The glide paths, inspired by asset‑allocation research Bogle championed, automatically shifted investors toward bonds and cash as retirement neared.
✨ Outcome：The crisis underscored that predetermined asset allocation, not security selection, largely drove differences in losses and recovery paths, validating Bogle’s focus on allocation over picking winners.
2
Vanguard Boglehead vs. Aggressive 30-Something in the GFC (2008)
During the 2008 financial crisis, many U.S. index investors on Vanguard’s Bogleheads forum compared outcomes. A 30-something investor following Bogle’s ‘age in bonds’ rule had ~30% in bond index funds and 70% in stocks when the S&P 500 fell over 50% from October 2007 to March 2009.
✨ Outcome：Their portfolio dropped roughly 30–35%, versus 45–55% for peers near 100% stocks. The smaller loss helped them avoid panic selling and stay invested, illustrating how age-based bond allocation can reduce behavioral mistakes in severe bear markets.
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