Circle of Competence: How to Invest Only in What You Understand
Your circle of competence is the set of businesses you understand well enough to judge their economics, risks and long-term prospects. Investing inside it means you only buy companies whose future you can reasonably estimate, and you say no to everything else. Warren Buffett popularised the idea, and it is one of the simplest ways to avoid big mistakes. The circle does not need to be large. You just need to know where its edges are.
Where this fits: the circle of competence is a mindset rule that sits in front of all the Five Criteria. If a business is outside your circle, you cannot honestly score it on any of them. It is a core part of learning to think like an investor.
What Is a Circle of Competence?
A circle of competence is the area where your knowledge gives you a realistic chance of judging a business correctly. Inside the circle, you understand how the company makes money, what could go wrong and why customers keep coming back. Outside it, you are guessing.
Buffett described the idea clearly in his 1996 letter to Berkshire Hathaway shareholders. He wrote that an investor does not need to be an expert on every company, or even many. You only need to be able to evaluate companies within your circle of competence. In his words, "The size of that circle is not very important; knowing its boundaries, however, is vital."
That last point is the one most investors miss. The danger is rarely what you know you do not know. It is what you think you know but do not.
Why the Circle of Competence Matters
It protects you from permanent loss
At Gingernomics we define risk as the permanent loss of capital. The most common cause of permanent loss is not volatility. It is buying something you misunderstood. Our guide to investment risk explains this in detail.
When a business is inside your circle, you are much more likely to spot a weakening moat, a bad acquisition or a balance sheet under strain before it becomes a disaster.
It lets you act when others panic
Understanding a business gives you the confidence to hold, or buy more, when the share price falls for reasons that do not affect long-term value. Without that understanding, every price drop feels like a warning. Our guide to using short-term price movements to your advantage depends entirely on this.
It saves time
There are thousands of listed companies. You do not need to analyse all of them. Buffett and Munger often talked about putting ideas into a "too hard" pile. Most businesses can go straight there, leaving your time for the few you can genuinely understand.
How Buffett Has Applied the Circle of Competence
Buffett has lived by this rule in public for decades. Through the late 1990s technology boom, he declined to buy fast-growing technology stocks, saying he could not predict which companies would still have strong economics years later. Many commentators thought he had lost his touch. When the bubble burst, his caution looked wise.
The circle can also grow. Berkshire Hathaway began buying Apple in 2016, and it became one of its largest holdings. Buffett has explained that he viewed Apple less as a technology bet and more as a consumer business with extraordinarily loyal customers. In other words, he found a way to understand it through a lens that was already inside his circle.
The lesson is not "never buy technology." It is to buy only what you can genuinely understand, and to be honest when you cannot.
Signs You Are Outside Your Circle
Sometimes you only notice you have left your circle once you are already holding the stock. Watch for these warning signs:
You rely on someone else's summary. If your thesis comes from a video, a newsletter or a friend, and you could not rebuild it yourself, you are outside.
You cannot say what would make you wrong. Every sound thesis has a clear point at which it breaks.
Every piece of news surprises you. Inside your circle, most results and announcements make sense in context.
You only understand the product, not the economics. Knowing that customers love something is not the same as knowing whether it earns a return on capital.
You feel anxious every time the price moves. Deep understanding tends to produce calm. Anxiety often means you are relying on the market to tell you whether you were right.
How to Define Your Own Circle of Competence
Your circle is personal. It comes from your work, your education, your hobbies and the products you use. Here is a practical way to map it.
Step 1: List what you already know
Write down the industries you have worked in, studied or followed closely for years. Include areas you understand as a customer. A nurse may understand hospital suppliers. A software developer may understand developer tools. A keen cyclist may understand bicycle components.
Step 2: Test each area with five questions
For each industry on your list, ask yourself:
Can I explain in two or three sentences how a typical company here makes money?
Do I know what drives customer choice, and why customers switch or stay?
Can I name the main competitors and explain who is winning and why?
Do I know what the industry looks like in a bad year?
Could I estimate, roughly, what a typical business here will earn in ten years?
If you can answer all five confidently, that area is likely inside your circle. If you struggle with two or more, it is outside for now.
Step 3: Be honest about the edges
Understanding a product is not the same as understanding a business. You may love a company's app and still have no idea whether it earns a return on capital. Our guide to different business models helps you close that gap.
Step 4: Write it down
Keep a short list of industries inside your circle and review it once a year. This becomes the first filter on your stock watchlist.
How to Expand Your Circle of Competence
Your circle is not fixed. It grows with deliberate study, but slowly.
Read annual reports across a whole industry. Reading the reports of four or five competitors side by side teaches you more than reading one company in depth.
Study the history. Learn what happened to the industry in the last two or three recessions. This is the best test of whether a moat is real.
Follow the cash, not the story. Work through the cash flow statement of each company to see how the business really works.
Talk to people in the industry. Customers, suppliers and former employees often understand the economics better than analysts.
Be patient. Expect it to take many months of steady work before a new industry is truly inside your circle.
Having worked in investor relations, I have seen how much context sits behind every quarterly number. Outsiders can learn a great deal, but it takes time and real effort. Do not treat a weekend of reading as competence.
A Worked Example: Two Investors, One Company
Imagine Company A, a hypothetical maker of specialised dental equipment. It has these round numbers:
ROIC of 18% for the past eight years
Net debt/EBITDA of 1.0x
Share count down 5% over five years
FCF yield of 6%
Investor 1 is a dentist. She knows which equipment brands dentists trust, how often clinics replace machines, how much training is needed to switch suppliers and how consumables are reordered. She can see that switching costs are high, which supports criterion 2. She can judge whether the 18% ROIC is sustainable. The business is inside her circle.
Investor 2 knows nothing about dentistry. He sees the same strong numbers but cannot say why they are strong or what might change them. If a new technology threatens the product, he will not recognise it until it shows up in the results. For him, the business is outside his circle, however good the numbers look.
Both investors see the same scorecard. Only one can trust it. That is the whole point.
How We Use This in the Five Criteria
The circle of competence is not a sixth criterion. It is the gate before the Five Criteria. Each criterion depends on understanding the business well enough to judge it.
Criterion | Why the circle matters |
1. Great business | You must know whether a high ROIC reflects a real advantage or a temporary boom |
2. Durable moat | You must be able to name the moat source and judge how long it will last |
3. Aligned management | You must know what good capital allocation looks like in this industry |
4. Sound balance sheet | You must know how bad a bad year can get in this industry |
5. Reasonable price | You cannot estimate intrinsic value for a business whose future you cannot forecast |
Our house rule is simple: if you cannot answer the five circle questions above, the stock does not get scored. It goes into the "too hard" pile, and you move on without regret.
Common Circle of Competence Mistakes
Confusing familiarity with understanding. Using a product every day does not mean you understand the business behind it.
Drifting outside the circle during a boom. Hot sectors tempt investors to buy what everyone else is buying. That is exactly when the edges matter most.
Assuming your circle is bigger than it is. Success in one area can create false confidence in another.
Treating the circle as fixed. Industries change. What you understood ten years ago may no longer be true.
Refusing to expand it at all. A tiny circle is fine, but a small amount of steady learning over many years can make it meaningfully larger.
Most of these mistakes share a root cause: overconfidence. The cure is a written list and the discipline to respect it.
Frequently Asked Questions
What is a circle of competence in investing? It is the range of businesses you understand well enough to judge their economics and risks. Investing inside it means only buying companies whose future you can reasonably estimate.
Who came up with the circle of competence? Warren Buffett popularised the term, including in his 1996 letter to Berkshire Hathaway shareholders. Charlie Munger also used the idea widely.
How big should my circle of competence be? Size matters much less than knowing the boundaries. A small circle you understand deeply beats a large one you only think you understand.
Can I invest outside my circle of competence? You can, but you are guessing. For businesses outside your circle, a low-cost index fund is usually a better way to get exposure.
Your Next Step
Once you know your circle, use the Five Criteria to score the businesses inside it. Then learn the research process step by step in how to research stocks. If you are just starting out, the 5-week beginner track will help you build your circle from scratch.
About the author: Cameron Hayes is a senior investor relations and finance professional who has worked in IR at Nasdaq Copenhagen-listed companies including Nilfisk and Maersk Drilling. He holds an MSc from Copenhagen Business School and a BCom from the University of Ottawa, and founded Gingernomics to teach individual investors the Five Criteria framework. More about Gingernomics.
The content on Gingernomics is for educational and informational purposes only and does not constitute financial advice. Always do your own research and consult a licensed financial advisor before making any investment decisions. Past performance is not indicative of future results.
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