Run Your Idea as a Simulation and Find What Breaks It

I want to simulate this idea before I commit to it:
[YOUR IDEA IN ONE LINE].
Before you simulate anything, build the world around it. Give me:
1. The cast. Every person or group whose decisions affect the
outcome, and what each one actually wants.
2. Their real behaviour. How each group decides, what makes them
say yes, and what makes them walk away.
3. The environment. Competitors, costs, timing, seasonality,
regulation, anything outside my control.
4. Every assumption you are forced to make because I have not
told you. List them explicitly and label them as assumptions.
5. The ten most likely ways this fails, ranked by how often that
failure kills ideas of this type.
Do not evaluate the idea yet. Just build the world. Where you need
a number I have not given you, ask me for it instead of inventing it.