Stating what would prove you wrong

A thesis is testable only when it names the evidence that would refute it, in advance.

• Investing
• Decision-making

2 ideas that carry it

• Post-mortemInvestingLetter located

  A bad year separated into its causes: which mistakes were mine and which were the market

  Separate a bad year into your errors and the market's mood, name the errors specifically, and say whether the method changes.

  Reviewing your own record, reading any manager's bad year, and the interview question about a mistake.

  From Giverny Capital's 2025 annual letter, on a year of underperformance · François Rochon

• TechniqueInvestingLetter

  State, for each holding, what would have to happen for the thesis to be right

  Write the thesis with its test attached: the variant view, the evidence, and the event that would confirm or refute it.

  Writing a stock pitch, reviewing a portfolio, and any investment committee that wants to know what would change your mind.

  From Greenhaven Road Capital's Q2 2026 letter, on changing how the portfolio is built · Scott Miller