Five Whys Examples
The best way to understand Five Whys is to see it in action. The three worked examples below cover a software production incident, an operations delivery failure, and a manufacturing defect — each with the full causal chain and the corrective action that addresses the root cause.
How to read these examples
Each example starts with a specific problem statement, then walks through the chain of “why” questions. The final step (marked Root cause) is where the corrective action targets. Notice that in every case the root cause is a systemic gap— a missing process, absent check, or unaddressed assumption — not a person’s mistake.
Example 1 — Software: production API outage
Context: A customer-facing API returns 500 errors for 45 minutes on a Tuesday morning. The on-call engineer restores service by rolling back a deployment. The team conducts a post-mortem using Five Whys.
Problem: The API returned 500 errors for 45 minutes
Corrective action: Define query performance acceptance criteria (maximum execution time, maximum connections consumed) and add an automated check to the CI pipeline. Separately, add a canary deployment step that routes 5% of production traffic to new releases before full rollout.
Example 2 — Operations: late customer deliveries
Context: An e-commerce team notices that orders placed on Fridays are consistently delivered one to two days later than promised. Customer satisfaction scores fall. The operations team runs a Five Whys.
Problem: Friday orders are delivered 1–2 days late
Corrective action:Update the email template immediately with accurate delivery windows. Then create a change management checklist item: “Review all customer-facing copy for accuracy” — required whenever shipping, collections, or fulfilment policies change.
Example 3 — Manufacturing: product defect rate spike
Context: A quality manager notices that the defect rate on a circuit board assembly line has risen from 0.4% to 2.1% over two weeks. The team runs a Five Whys to find out why.
Problem: Circuit board defect rate rose from 0.4% to 2.1%
Corrective action: Restore the previous oven profile while a new profile is validated across all joints. Update the ECO process to require full thermal sign-off before any oven profile change reaches production.
Key patterns across all three examples
Reading across the examples, a few patterns stand out that characterise effective Five Whys analyses:
- The root cause is always a missing process or check, not a person. Nobody is at fault in any of these examples; the systems in place allowed failures to happen.
- The corrective action targets the root cause, not the symptom. Replacing the belt, updating the email template, or restoring the oven profile are necessary short-term fixes — but the lasting value is in the process change that prevents recurrence.
- The trigger is always something observable and specific. Vague problem statements (“quality is declining”) would have produced vague root causes. Precision at the start pays off at the end.