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Lean 5-Why Root Cause Tool

Start with a clear symptom, then drive each why deeper. The tool classifies every answer by cause layer — human, process, or system — and nudges you past blame until the chain reaches a system cause worth acting on.

Instructions

How to use this app

  1. State the problem as an observed symptom, not a guessed cause.
  2. Answer each why in plain operational language. The colored badge tells you which layer you are at — human, process, or system.
  3. Watch for the amber nudge: if you are stuck at “someone forgot,” keep asking what process or system condition allowed it.
  4. Mark each answer as a fact or an assumption. Assumptions stay flagged in red until you verify them at the gemba.
  5. Add alternative causes where a why has more than one plausible answer, and switch branches to explore each path.
  6. When the chain reaches a fundamental system cause, mark it as the root cause, then capture the countermeasure, owner, and verification. Use Read it back to sanity-check the logic and Copy report to save the record.

This app helps structure thinking. It does not prove causation by itself. A real root cause still needs engineering and process verification before corrective action is finalized.

What This Lean 5-Why Tool Helps You Do

This tool helps teams move from a symptom statement to a disciplined root-cause conversation. It generates a structured why chain from the problem description, lets users capture each answer step by step, and mark the point where the team believes the underlying cause has been reached.

Use it for recurring defects, process escapes, safety concerns, delivery failures, or team troubleshooting sessions where the first explanation is usually too shallow.

Core 5-Why Logic

Step Question Purpose
Problem statement What failed, where, and how often? Starts the chain with a factual symptom instead of blame.
Why 1 to Why 5 Why did the previous condition occur? Pushes the discussion past surface causes into process and system logic.
Root cause mark Which answer best explains the failure mechanism? Creates a defined handoff point into corrective action planning.

Worked Example

A shipment arrives with missing labels. Why 1 may show the operator skipped the label check. Why 2 may reveal the check was not built into the station flow. Why 3 may reveal the standard work was revised but not retrained. By Why 4 or Why 5, the team is no longer talking about one person making a mistake. It is talking about a broken management system.

That shift is the reason the method works. The tool makes the chain visible enough to challenge weak logic before the team acts on the wrong cause.

How to Interpret the Output

Lean 5-Why Frequently Asked Questions

Do you always need exactly five whys?

No. Five is a forcing function, not a law. Some issues resolve in three whys and some need more because the system cause is deeper.

What is the most common 5-Why mistake?

Stopping at operator error. If the answer is simply that someone forgot, the team has not yet found the process condition that allowed the failure.

When should 5-Why not be used alone?

Use more than 5-Why when the problem has several interacting causes, poor traceability, or conflicting evidence. That is where Fishbone, Pareto, or 8D adds structure.

Who should participate in a 5-Why session?

Include the people who know the work directly, plus quality or engineering support where needed. The best chains come from those closest to the process.

What happens after the root cause is chosen?

The team should define corrective action, ownership, timing, and effectiveness checks. Root-cause identification without follow-through is only diagnosis.

Related Templates and Guides

Read the 5-Why Guide

Use the guide for facilitation tips, branching logic, and the difference between symptom, direct cause, and system cause.