The Power of Knowing What You Don't Know
In 1999, the dot-com bubble was inflating wildly. Tech stocks were doubling every month. People mocked Buffett for missing out. His response: "I don't understand technology, so I don't invest in it."
Three months later, the NASDAQ crashed 78%. Buffett's Berkshire was barely scratched. The man who "missed the tech boom" was vindicated spectacularly.
"What counts is not how much you know, but how realistically you define what you don't know."
What Is the Circle of Competence?
Your circle of competence is the set of industries, business models, and companies that you truly, deeply understand. Not "I've heard of it" — but "I can explain exactly how it makes money, what risks it faces, and what it'll look like in 10 years."
💡 Inside vs Outside the Circle
- Inside: You understand the product, competitive dynamics, and financial model
- Inside: You can identify when the market is wrong about this business
- Outside: You rely on tips, headlines, or other people's opinions
- Outside: You can't explain why the stock should be worth more than today's price
- The edge: recognizing exactly where the boundary is
Duan Yongping's Discipline
"I don't invest in biotech because I can't access it, can't use it, can't understand it. Sticking to what I know is not cowardice — it's wisdom."
Duan's portfolio is famously concentrated: Apple, Moutai, Tencent. All businesses he can explain in one sentence. He turns down hundreds of "opportunities" per year that fall outside his circle.
How to Expand Your Circle
The circle of competence isn't fixed — it can grow. But it grows slowly, through deep study and real experience, not through reading headlines.
💡 Expanding Your Circle
- Study one industry deeply for 6-12 months before investing a single dollar
- Read 10+ annual reports of companies in that industry
- Talk to customers, suppliers, and competitors if possible
- Start with a tiny position to 'earn your education' with real skin in the game
- Build mental models — what drives revenue, costs, and competitive advantage?
💡 Circle of Competence — Key Summary
- Know what you know, and more importantly, know what you don't know
- Buffett avoided tech in 2000, dodged a 78% crash — by staying in his circle
- Duan: 'I can't understand biotech, so I don't invest in it'
- Your circle can expand, but only through deep, sustained study
- The edge comes from knowing exactly where your circle ends
- Better to earn 15% on what you understand than lose 50% on what you don't