📖Joel Greenblatt
Position Sizing Discipline
Size positions based on conviction and risk.
The size of your position should reflect your conviction and the risk involved. Never bet so large that a single mistake can wipe out your portfolio.
🏠 Everyday Analogy
📖 Core Interpretation
Joel Greenblatt views portfolio construction as risk architecture. Allocation, position sizing, and rebalancing rules determine whether you can stay disciplined across market regimes.
💎 Key Insight：Proper position sizing prevents catastrophic losses.
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❓ Why It Matters
Without portfolio rules, decisions become reactive and concentrated. Sustainable returns come from controllable risk exposure, not one-off bets.
🎯 How to Practice
Set target allocation by risk tolerance, rebalance by rules rather than headlines, and prevent hidden concentration from dominating portfolio behavior.
⚠️ Common Pitfalls
Diversifying superficially without true risk balance
Skipping rebalancing rules and drifting style
Judging portfolio health by short-term returns only
📚 Case Studies
1
Magic Formula Small-Cap Portfolio (2012)
An investor built a 20–30 stock portfolio of high-ROC, cheap small caps per Greenblatt’s method, then suffered early underperformance and volatility.
✨ Outcome：Maintaining the rules-based portfolio for several years led to strong excess returns versus the market, illustrating the payoff of disciplined holding and rebalancing.
2
Dot-Com Bubble Peak (2000)
Portfolio heavily tilted to soaring tech stocks after big gains in 1999.
✨ Outcome：Annual rebalance trimmed tech, added undervalued cyclicals; reduced subsequent crash losses and improved 5-year risk-adjusted returns.
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