First-Principles Thinking
04

Separating Facts From Assumptions

The hardest part of first-principles work is noticing what you're treating as a fact when it's actually an inherited belief. Here's how to spot the difference.

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What counts as a fact

  • It can be measured or directly observed.
  • It would still be true if every competitor disappeared tomorrow.
  • You can point to the source, not just the conventional wisdom.
  • Reversing it produces an obviously wrong outcome, not just an unfamiliar one.

Common 'facts' that are actually assumptions

  • 'Customers want this feature' , usually means a few loud customers asked.
  • 'The market is X billion dollars' , usually a top-down analyst report, not your reachable market.
  • 'We need a sales team' , usually means the founder doesn't want to sell anymore.
  • 'Investors expect Y' , usually one investor's preference generalized.
Write down every claim driving a decision. Mark each one as Fact, Assumption, or Inherited Belief. You'll be shocked how few facts you have.