Look Before You Leap
Name the assumption that would kill you
Your plan has maybe fifty moving parts. But two or three of them, if false, sink everything. Do you know which ones?
Every plan rests on beliefs you're quietly treating as facts. The most dangerous ones are invisible precisely because they feel too obvious to question.
Every venture rests on two or three make-or-break beliefs — Critically Important Assumptions. If any one is false, the whole idea is far weaker than it looks. Your job is to find them, and attack the scariest one first — not the comfortable one.
- List every belief your plan needs to be true — customers want it, will pay X, can reach you, will come back.
- Sort them into two piles: value (will people love it?) and growth (will more people keep coming?).
- For each belief, score two things: how likely it is false, and how fatal it is if it turns out false.
- Circle the belief that scores high on both — likely false AND fatal. That is your killer assumption.
- Test that one first. The comfortable assumptions can wait their turn.
A yoga studio's plan hides three bets: (1) enough people nearby want studio yoga, (2) they'll pay 300 a month, (3) they'll keep renewing past month three. Bet 3 is both shaky and fatal — a studio full of one-month quitters dies. So test retention BEFORE signing a lease, by pre-selling annual memberships.
Dean Kamen poured over $100 million into a brilliantly engineered self-balancing scooter, forecasting around 50,000 sales a year — treating 'a mass market exists at $5,000' as a fact instead of testing it.
→ It sold roughly 30,000 in five years. The technology worked flawlessly; the mass market at that price simply never existed, and production ended for good in 2020.
The killer assumption — 'the crowd will buy this' — was never cheaply tested. No amount of money or engineering rescues a market that isn't there.
The comfort trap: owners test the assumption they're already confident about, because confirming it feels good — and quietly avoid the terrifying one. Invert this. Hunt the belief you are most afraid is wrong.
Say your idea out loud, then finish this sentence: 'This only works if ___ is true — and I have not actually checked it.' Whatever fills that blank is where to start.
Don't test what's comfortable; test what's fatal. Rank your beliefs by 'likely false' times 'fatal if false,' and buy the answer to the top one first.
Write your three biggest assumptions on paper, mark each 'value' or 'growth,' and circle the one that would hurt most if it's wrong. That circle is this week's mission.
Look Before You Leap