Assumption Storming
A structured exercise for surfacing and evaluating the hidden assumptions underlying a plan, strategy, or product idea. Participants list all the assumptions the plan depends on, then map them by importance (how critical is it if this is wrong?) and certainty (how confident are we this is true?). High-importance, low-certainty assumptions are the critical risks to test.
How to run it
- 1
Present the plan, strategy, or product concept.
- 2
Ask: 'What must be true for this to work?' Have everyone silently write assumptions on sticky notes (5 min).
- 3
Share assumptions and cluster similar ones.
- 4
Draw a 2x2 matrix: x-axis = certainty (low → high), y-axis = importance (low → high).
- 5
Plot each assumption on the matrix.
- 6
Focus attention on the top-left quadrant: high importance, low certainty. These are your riskiest assumptions.
- 7
Design experiments or research to validate or invalidate the riskiest assumptions before committing.
Tips
Teams often confuse opinions with assumptions.
An assumption is something that hasn't been proven yet.
Push back on 'We know users want this' — do you actually know, or is that an assumption?
Variations
Run a 'Leap of Faith' variant (from Lean Startup) focused only on the two most critical assumptions to test. Add a third axis (testability) to prioritise which assumptions you can actually test quickly.
Where it fits
Frequently asked questions
When should I use Assumption Storming?â–¾
Use Assumption Storming when you want to: Product discovery; Business model validation; Strategy risk assessment; Lean startup experiments.
How long does Assumption Storming take?â–¾
Assumption Storming typically takes 30–60 minutes.
How many participants does Assumption Storming work for?â–¾
Assumption Storming works best for groups of 2–20 participants.
What materials do I need for Assumption Storming?â–¾
To run Assumption Storming you will need: sticky notes, markers, 2x2 matrix (importance vs. certainty).
How difficult is Assumption Storming to facilitate?â–¾
Assumption Storming is rated intermediate — some facilitation experience is helpful.
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