IdeationIntermediate

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.

Duration

30m–1h

Group size

2–20 people

Materials

sticky notes, markers, 2x2 matrix (importance vs. certainty)

Origin

Community

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

Product discoveryBusiness model validationStrategy risk assessmentLean startup experiments

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Method descriptions on Workshop Weaver are original content written by our team, based on established facilitation practices.