CODEXCard 6 of 12 · 12 Mental Models
Circle of competence
Know the edge.
The circle of competence is a model Warren Buffett and Charlie Munger used to describe the limits of reliable judgment. Inside the circle are subjects you understand deeply enough to make good calls. Outside it are subjects where you may feel informed but are really guessing. The goal is not to have a huge circle, but to know its boundary precisely.
Munger and Buffett used this to decide what not to invest in. They were willing to pass on whole industries simply because they did not understand them well enough, even when others were making money there. That restraint kept them out of many mistakes. It also freed them to act with conviction when an opportunity fell squarely inside what they knew.
The common mistake is confusing familiarity with competence. Having read a few articles or followed a topic for a while can create a feeling of understanding that is not backed by results. A better test is your track record: in areas of real competence, your predictions and decisions turn out right more often than chance.
This model works well with inversion. Asking where you are most likely to be fooled helps map the edge of your circle more honestly than asking where you are strong.
Example
You are good at managing your household budget and decide to pick individual stocks after watching a few investing videos. The confidence feels the same, but the skill is not. Recognising that boundary might lead you to a simple index fund while you build real knowledge slowly.
Try it this week
List three areas where you make decisions often, and mark honestly which ones your track record shows you are good at.
From 12 Mental Models (Charles T. Munger · 1995).
