How do I practice assumption testing?

The most direct way to practice assumption testing is through a focused exercise: 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.

Common pitfall: Listing only the assumptions you are already aware of — the safe, obvious ones. The assumptions that destroy plans are the ones so deeply embedded you mistake them for facts. If your assumption list feels comfortable, you haven't gone deep enough. The real practice is surfacing what you don't know you're assuming.

This practice connects to Phase 10 (Externalization Mastery) — building it as a repeatable habit compounds over time.