The Five Whys

Five Whys is “a question-asking method used to explore the cause/effect relationships underlying a particular problem. Ultimately, the goal of applying the 5 Whys method is to determine a root cause of a defect or problem”. Developed by Taiichi Ohno–one of the inventors of the Toyota Production System–the oft-cited example is as follows:

  • My car will not start. (the problem)
  1. Why? – The battery is dead. (first why)
  2. Why? – The alternator is not functioning. (second why)
  3. Why? – The alternator belt has broken. (third why)
  4. Why? – The alternator belt was well beyond its useful service life and has never been replaced. (fourth why)
  5. Why? – I have not been maintaining my car according to the recommended service schedule. (fifth why, root cause)

I was introduced to Five Whys in a post by Joel Spolsky back in early 2008 detailing their post-mortem examination following a system outage (which also looks at the problems with SLAs).

Entrepreneur Eric Ries recently wrote a comprehensive post detailing how to conduct a Five Whys root cause analysis which I suppose acts as an update to this previous post of his where he introduces his readers to the Five Whys concept and adds this important caveat:

The next step is this: you have to commit to make a proportional investment in corrective action at every level of the analysis.

Five Whys is a concept I’ve attempted to–somewhat successfully–apply to myself and my development. When I make mistakes or when I don’t understand something I ask why until I find the root cause of my error, the misunderstanding, or the negative reaction. Similarly, GigaOM’s Mike Speiser recommends Five Ways as one of the four techniques¬†you should embrace in order to become at ease with ideas that make you uncomfortable.

You may find that your reaction is more about protecting existing orthodoxy or the source of the idea than it is about the merits of the particular approach at hand.

And of course, to end in a joke, you don’t want to ask why too many times (via Kottke).



2 responses to “The Five Whys”

  1. […] There is more about Toyota’s lean production system here. And the concept of Kanban is explained here. And there is a nice post on the five whys used at Toyota here. […]

  2. I thank you for the applied example on five whys and for its clarity. I have recently published a presentation on slideshare that tackles the shortcoming of five whys and called for its extension to eight whys. I gave reasononig for this extension. The link is: