What does it mean that externalize your assumptions?

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.

Try this: Pick one active project or decision. Set a timer for ten minutes. Write down every assumption you can identify — about the people involved, the timeline, the resources, the market, the technology, your own capabilities. Aim for at least fifteen. Then mark each one: (K) for assumptions you have evidence for, (U) for assumptions you are uncertain about, and (L) for assumptions that would be catastrophic if wrong. Any assumption marked both U and L is your highest-priority assumption to test this week.