What is assumption mapping?

Assumption mapping is a concept in personal epistemology: Assumptions you never write down are assumptions you never question. Every plan, decision, and belief rests on invisible premises — and the invisible ones are the ones that destroy you.

Example: A startup spends eighteen months building a product around the assumption that enterprise buyers will pay for a self-serve onboarding flow. Nobody writes down this assumption. Nobody tests it. When they finally talk to buyers, they discover enterprises require white-glove implementation — not because self-serve is bad, but because procurement processes mandate human touchpoints. The assumption was never wrong in theory. It was wrong in context. And because it was never externalized, it was never examined until $2M was gone.

This concept is part of Phase 10 (Externalization Mastery) in the How to Think curriculum, which builds the epistemic infrastructure for externalization mastery.