Category: Risk identification & assessment · Reviewed by Matt Bartlett, Director · Founder · Last reviewed
Five Whys
The Five Whys is a simple iterative questioning technique used in root cause analysis. It was developed by Sakichi Toyoda and adopted as a core problem-solving tool within the Toyota Production System.
Method
Starting with a problem statement, the analyst asks “why?” and uses the answer to ask the next “why?”. After approximately five iterations the question typically reaches a systemic, actionable root cause. The number five is a heuristic — sometimes three is enough, sometimes seven.
Worked example — fleet motor claim
Why was the lorry damaged? Because the driver reversed into a bollard.
Why? Because they did not see it in the mirror blind spot.
Why? Because the reverse camera was broken.
Why? Because pre-shift checks were not completed.
Why? Because there is no enforced check-list and supervisors are not auditing compliance.
The action plan targets the systemic gap (5), not the driver (1).
Limitations
Linear “why?” questioning can miss parallel contributing causes — pair with a fishbone diagram for complex incidents.
Outcome depends heavily on the analyst’s framing of each “why”.
Best used alongside, not instead of, fact-based investigation.
References
Ohno, T. (1988). Toyota Production System: Beyond Large-Scale Production. Productivity Press.
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