Finding
Test forward from the person’s intention and backward from the final result. Identify the first point where the expected response stops rather than assuming the device displaying the symptom is at fault.
How the mechanism works
Layered testing separates the endpoint, upstream control path, account relationship and environmental dependency while preserving working parts as evidence.
Evidence boundary
Do not dismantle a working pathway merely to make every management screen look consistent. Record uncertainty and change only what evidence supports.