Quick Read
Position size must match knowledge depth: a 2% portfolio position tolerates edge-of-competence understanding, while a 25% position demands the five-question test be answered without hesitation, because a 50% drawdown in a concentrated holding forces a 14% recovery grind across the remaining portfolio.
Your circle of competence has three rings—business mechanics (60-second explanation, customer, moat, costs, single fatal risk), industry economics, and the danger zone—and holding a stock larger than 5% of your portfolio without being able to answer all five questions means you are sized larger than your knowledge.
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On a recent episode of The Investing for Beginners Podcast titled Back to the Basics: Circle of Competence, co-host Stephen Morris pitched a simple test for whether you actually understand a stock before buying it. He asks: “Can I explain the company in 60 seconds? Can I explain who pays them? Can I explain their finances, their expenses? Can I explain their moat? Can I explain what will kill them overnight as a company?” If you cannot answer those five questions cleanly, the investment falls outside your circle of competence.
The stakes are practical. Buying a stock you cannot explain in plain English means paying retail for someone else’s story. When the story breaks, you have no framework for deciding whether to hold, add, or sell. And that is when permanent capital loss happens.
The Framework Holds Up, Position Size Multiplies It
Morris’ three-circle test is sound advice and the cleanest plain-English version of Warren Buffett’s circle of competence.
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The inner circle covers the five business questions. The middle ring covers industry economics and product knowledge. Anything past the second ring is the danger zone, where you either commit to deeper research or pass. The framework forces you to separate brand recognition from business understanding.
The piece most retail investors miss is what co-host Andrew Sather adds: position size determines how much knowledge you actually need. “If we’re talking about, you know, I’m buying 100 companies, you probably don’t need to know those companies very well. If you’re putting a quarter of your portfolio in a company, hopefully you know it as well as Warren Buffett knows Coca-Cola.”
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