The 5 Whys approach to root cause analysis is by no means new, nor does it originate in Six Sigma. Yet it is often used in the Analyze phase (of DMAIC [Define, Measure, Analyze, Improve, Control]), especially when significant data on the Xs is not available.

Most of us have been there – we gather the team of experts, draw the fishbone, and start brainstorming. We ask why five times until we get to the root cause. Then maybe rack and stack the causes using some sort of matrix, rating each cause byease of correctionvs. impact on the problem. Sometimes we don’t even need to ask why five times to get to the answer. One or two is all it takes.

Recently, I had the opportunity to (i.e., was required to) take a class on a specific root cause analysis method. In this class we talked about asking why many more times than five, taking it all the way back to theology or absurdity, whichever comes first. We were taught to search for as many causes as we could find, taking time to validate each and every one before ruling it out and moving on. No rack and stack matrix would do – we needed to find the root causes, and work to develop solutions that involved true error-proofing, preventing these issues from recurring. Or else enlighten management to the risks we were accepting by choosing not to address certain causes.

Hundreds of past fishbones and 5 Whys flashed before my eyes – suddenly they seemed somewhat inadequate. Memories of glitches in Improve as we piloted process changes, due to a step or factor we overlooked in Analyze. It was a teachable moment for sure.

I don’t suppose Taichi Ohno literally meant only ask 5 times to get to the root causes of problems, but the takeaway from this experience reminded me that sometimes the right number of why’s is not 5, but 25 or 125.