What the 5 Whys method is
The 5 Whys is a simple root-cause analysis technique created by Sakichi Toyoda: ask "why" repeatedly in the face of a problem, using each answer as the basis for the next question, until you reach the real root cause — usually between the third and fifth question.
A full worked example
Why did the machine stop?
Because a fuse blew from overload.
Why was there an overload?
Because the bearing wasn't sufficiently lubricated.
Why was lubrication insufficient?
Because the oil pump wasn't pumping enough.
Why did the pump fail?
Because the shaft was worn from metal-shaving buildup.
Why was there metal shaving in the pump?
Because there's no filter on the oil intake — the root cause.
The first answer is almost always a symptom; the root cause is usually two or three questions deeper.
Common mistakes when applying it
- Stopping at the first or second answer, still a symptom
- Blaming a person instead of investigating the process or system
- Doing the exercise alone, without the person who actually does the task
- Not validating the root cause with data before implementing a solution
About the author
Lean Manufacturing & Behavioral Management Specialist
Over 20 years in the automotive and metalworking industries (GM and Dana), Lean Manufacturing practitioner since 2006. SENAI instructor and mentor in Brazil’s Brasil Mais Produtivo program, delivering consulting, training and audits for 50+ companies, combining quality, productivity and people development.