Five Whys Plus Build an evidence-linked causal chain from a known proximate fault to an actionable systemic root, then prescribe a countermeasure that would have blocked it. When to Use - A fault is already localized to a component, path, or subsystem. - The proximate cause is known, but recurrence or systemic root is not. - Prior symptom-only fixes failed and the failure returned. - You need prevention that addresses why the proximate cause was possible. When NOT to Use - Fault is not localized or multiple candidate causes remain — discriminate first. - Root is evidenced and actionable — fix…