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 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.