Find the Boundaries
Name constraints, assumptions, invariants, and what is deliberately outside the first version.
Name the ConstraintsNot started
Time, scale, regulation, team knowledge, and required integrations remove options before architecture begins.
Make Assumptions VisibleNot started
An assumption is a temporary answer used to move forward. Write it down with a way to verify it.
Protect the InvariantsNot started
Some properties cannot be traded away even in a small first version. State them before simplifying.