Stage 3
If margins break at scale, the model fails.
Use this stage to test whether revenue, cost, and founder load can support real growth.
Use this before scale, fundraising, new hiring, or committed operating spend.
System Flow
Problem → Product → Model
Problem
Problem–Solution Fit
If the problem is weak, every signal above it misleads.
Product
Product–Market Fit
If users do not return, you do not have product–market fit.
Business Model
Business Model Fit
If margins break at scale, the model fails.
If one breaks, everything above misleads
- Product signals are invalid without a real problem.
- Business signals are invalid without real product pull.
Current Stage
Use this stage before scale, spend, or fundraising
Business Model Fit
If the economics depend on founder effort or fragile margins, the model is not ready.
When to use
After product pull exists and before you treat growth as durable.
How ProductBooks works
- Run the evaluator.
- Identify what still scores zero.
- Generate the missing evidence.
- Re-run the same stage before moving on.
What this stage decides
Keep the decision boundary narrow. Everything outside it stays outside.
Decides
Whether unit economics support sustainable operation.
Does not do
Optimise pricing strategy.
Decides
Whether costs hold as revenue grows.
Does not do
Improve margins for you.
Decides
Whether revenue persists beyond founder effort.
Does not do
Help you "pass".
Evidence Rules
Strict rules only. No interpretation layer.
What counts
- Observed unit economics before projections.
- Traceable acquisition cost before blended assumptions.
What fails fast
- Durable revenue before one-off selling.
- Missing proof still blocks scale confidence.
Generate Missing Evidence
Operators generate proof. They do not soften the verdict.
Unit Economics Reality Operator
GENERATEMeasure whether each customer produces positive contribution margin from observed data.
Used to improve
The scoreable gaps this evaluator surfaced.
CAC Traceability Operator
GENERATETrace acquisition cost back to specific customers and acquisition actions.
Used to improve
The scoreable gaps this evaluator surfaced.
Revenue Durability Operator
GENERATEMeasure whether revenue persists without repeated manual sales effort.
Used to improve
The scoreable gaps this evaluator surfaced.
Founder Dependency & Load Operator
GENERATEMeasure whether the model still holds when the founder steps out of the loop.
Used to improve
The scoreable gaps this evaluator surfaced.
Run Business Model Fit
Start with evidence you can show. Missing proof still scores zero.
What to do next
Once the model holds, consolidate the system into one report.
Use the Fit Report Generator to combine stage verdicts, evidence gaps, and next actions into a single system view.
Go to Fit Report