The Three-Circle Test: Why You Don’t Need to Be the CEO to Pick Winning Stocks

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.

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.”

Story Continues

Consider a 42-year-old with $150,000 in a taxable brokerage account. A 2% basket position in a cybersecurity name is $3,000. If the company gets disrupted and the stock drops 50%, the loss is $1,500, or roughly 1% of the portfolio — a manageable setback.

Flip the same trade into a 25% conviction position and the dollar exposure jumps to $37,500. The same 50% drawdown is $18,750, or roughly 13% of the entire portfolio. The rest of the account then has to grind out roughly 14% just to climb back to even.

The test scales with concentration. A 1% basket position lets you operate near the edge of circle two. A 25% position requires you to be deep inside circle one, with answers to all five of Morris’s questions ready without opening a browser tab.

Who Should Actually Use This Test

The framework fits the investor running a concentrated portfolio of eight to 20 individual stocks, especially anyone allocating more than 10% to a single name. It also fits sector specialists: a nurse evaluating a medical device maker, an engineer reading a semiconductor 10-K, a small-business owner sizing up a payments company. Domain expertise is a real edge when paired with honest sizing.

The test matters less for the broadly diversified investor holding a total-market index fund. They are buying the system, not individual theses. It also tightens for fast-moving sectors. As the podcast notes, products in cybersecurity can become obsolete tomorrow, which means yesterday’s deep knowledge ages into next quarter’s stale thesis. Generative AI carries the same problem.

Your Action This Week

Open your brokerage account and rank holdings by position size. For any single stock above 5% of the portfolio, write five lines on paper: the 60-second business explanation, the customer, the moat, the cost structure, and the one risk that could end the company. If you cannot fill in all five from memory, you are sized larger than your knowledge. Either resize toward your knowledge level or commit to the research before the market forces the decision for you.

The one thing to remember: the three-circle test rewards honest position sizing far more than it rewards raw intelligence.

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