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thinking-five-whys-plus

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When a fault is localized and the proximate cause is known but the systemic root is not, chain evidence-linked whys with a counterfactual stop and a countermeasure.

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 it.
• No evidence can answer the next "why" — gather evidence.
• One-off error without a process, tooling, or design enabler.
• Selective defect needing IS/IS-NOT analysis.
• Forward failure forecasting before commitment.

Skill page

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