How Warren Buffett's Circle of Competence Applies to Tech Stack Decisions

Warren Buffett has a simple framework that's earned him over $100 billion: only invest in things you truly understand. He calls it the Circle of Competence. Everything you have deep, earned knowledge about sits inside the circle. Everything else is outside it. The key isn't making your circle bigger — it's knowing exactly where the edge is and refusing to pretend otherwise. Buffett has said he doesn't invest in technology companies he can't fully evaluate. This isn't false modesty. It's discipline. And watching his returns over six decades, it's hard to argue with the results. I've been thinking about this principle for two years, and I'm now convinced it's the most underused mental model in software engineering. Because the pattern of failure Buffett identifies in investing — people getting into trouble because they operate outside their competence without realizing it — maps almost perfectly onto how engineering teams choose technology. The Circle of Competence, Defined Buffett's par