Emphasizes diverge → merge → hypotheses to verify, with facilitation prompts and group exercise tips.
Two fishbones for one defect (floor vs engineering views); mark branches needing data validation (scatter/stratification) before D4.
Pair with 5 Why but keep distinct purposes.
Avoid endless unweighted causes; merge duplicates but keep evidence pointers.
Update the diagram after verification — do not freeze unvalidated branches.