📖Joel Greenblatt

Hold a Portfolio

🌿 Intermediate★★★★☆

Hold 20-30 stocks for optimal diversification.

💬

Hold 20-30 positions to reduce single-stock risk while maintaining concentration in best ideas.

— The Little Book That Beats the Market，2005

🏠 Everyday Analogy

Portfolio construction is like building a team. You need complementary roles, not eleven strikers chasing the same ball.

📖 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：Below 20 stocks, single-position risk becomes too high. Above 30, you dilute returns without meaningfully reducing risk. Greenblatt's research shows 20-30 positions capture most diversification benefits while maintaining concentration in your best ideas. This sweet spot balances risk management with return potential. Most retail investors are either too concentrated or too diversified.

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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.

🎙️ Master's Voice

You don't need to own 50 stocks. A few great ideas are enough.
Greenblatt concentrates. A handful of great investments beats broad diversification.

⚔️ Practical Guide

✅ Decision Checklist

  • Am I too diversified?
  • Are these my best ideas?
  • Should I concentrate more?

📋 Action Steps

  1. Focus on best ideas
  2. Limit diversification
  3. Concentrate conviction

🚨 Warning Signs

  • Over-diversification
  • Too many positions
  • Diluted conviction

⚠️ 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
Holding Through the Financial Crisis (2008)
An investor following Greenblatt’s Magic Formula held a diversified portfolio as the 2008 crisis caused steep declines across value names.
✨ Outcome：By holding and rebalancing annually instead of selling in panic, the portfolio recovered and outperformed the S&P 500 over the following years.
2
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.

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