The second-richest investor in American history built his entire edge on one habit, and it wasn't stock picking. It was reading.

Charlie Munger, Warren Buffett's longtime partner at Berkshire Hathaway, was known for a way of thinking that set him apart from most professional investors, who tend to specialise deeply in finance and little else. Munger did the opposite. He read widely across psychology, physics, biology, mathematics, and history, and deliberately built what he called a latticework of mental models — the best-tested ideas from every serious field, ready to pull out and apply to whatever problem was in front of him.

His own explanation was disarmingly humble for a man of his stature. He said he believed in mastering the best that other people had already figured out, rather than sitting down and trying to invent everything himself — because, in his words, nobody is that smart on their own.

This runs against the instinct most people bring to markets. There's a quiet pride in wanting to discover an original edge, a unique insight no one else has found. Munger's own record suggests the opposite path was more reliable: identify the strongest, best-tested ideas that already exist across every discipline, understand each one properly, and apply the right one to the situation in front of you.

Two of those borrowed ideas did more work for him than almost any others. The first was staying inside what he called a circle of competence — a deliberately drawn boundary around what you genuinely understand well enough to judge correctly, and a firm refusal to make important decisions outside it, no matter how attractive the opportunity looks. The second was a habit called inversion: instead of only asking how to succeed, ask just as seriously how it could fail, and work backward to remove those failure paths first, before ever asking how to add cleverness on top.

Neither idea is complicated to state. Both are unusually hard to practice, because both require honesty about your own limits that ambition tends to resist.

Munger also spoke often and admiringly of Darwin's own habit of recording evidence against himself, because he recognised in it the same trait he'd spent a lifetime trying to build in himself.

None of this required Munger to be the most original thinker of his era. It required him to be, by his own account, an unusually disciplined student of everyone else's best thinking — applied with a patience that outlasted nearly every competitor who tried to out-clever him instead.