Is 5 Times Enough to Ask “Why?”

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.

Handpicked Content:   The 5 Whys: A Simple Tool in Value Stream Analysis

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.

Comments 11

  1. Ben Davis

    Agreed. Primary causes tend not to be so elusive when tenacity is applied to the ’Whys’.

    PS. I like the inference that theology provides no useful answers!

  2. EvieM

    Good food for thought. Agree you need to be satisfied that you’ve identified true root cause otherwise what’s the point? Using these tools as a tick box exercise or without a clear objective is poor practice and a waste of everyone’s time.

    However, in the absence of significant data, no matter how thorough you are brainstorming techniques will only give you potential root causes? For all potential root causes you’d still need to establish a cause and effect to be satisfied you were addressing your problem statement?

  3. Amit MIsra

    We know in this new world of technology where nano is taking charge from micro ones 5 times asking why is not enough to get REDEX.

    In my observations we need more digging to get into the roots.



  4. James Considine

    The idea that there is but a single critical X is one we’d all do well in abandoning – in transactional processes especially, the root causes (plural) are often not in a metric or measurement system. But they are there nonetheless and when overlooked, often show themselves in our process outputs.

  5. Paul Hesselschwerdt

    Completely agreed with your ’endless whys’. We have found that using this approach is a great tool for creative thinking. As for Ohno, I suspect that like many of the tools he simply used it as shorthand for fixing anything and everything. We do the same, using 5 whys to find root causes of lost sales, failed drug experiments, etc.
    I am curious about how many different ’out of the box’ applications people have used 5 whys for

  6. Nick

    Ben Davis, what does your Post Script mean?
    Where is this inference in the original post?
    And why do you like it?

  7. Attila Dobai

    Great article. It is important for us to remember that 5-whys was not meant to be taken literally. It is really just a tool to help us get to the root cause. That may take 2-whys or 200-whys. The number of times you ask is not as important as why you ask.

  8. Fred Friend

    The five or more ’whys’ is a great investigative tool. We also use it exensively in performance consulting (training). A good companion is the Kepner & Trego ’Rational Manager’ model for defining root cause as the answer to a ’why’ that would ’always’ explain the error if it were present and ’always’ explain the lack of error when it was absent (I oversimplify – check it out for yourself).

  9. chak

    In my experience,even going to the 3rd level ’Why’ was found difficult,impractical,just woolgathering,guessing!

    If we know that behind each ’WHY’ ,we should support it with the corresponding RPN number ’actually happened as seen fm factual data/control charts&contol plan with the installed poke yoke’,then ,even getting upto 5th "why’ level will take u to Himalayas& u will surely see the ’theological’ BRAHMAN!


  10. Ben Davis

    Hi Nick,

    The comment to which my post-script referred was:

    "In this class we talked about asking why many more times than 5, taking it all the way back to theology or absurdity."

    The clear inference is that theology and absurdity are equatably useless end-points from the perspective of root cause analyses leading to actionable results (I’m a pearlist, if that helps explain my position).

    I like this because theology sits well within the realms of guessing or wishful thinking and I hope that everyone is aware of the dangers there.

  11. HF-Chris-Vallee

    It is not about how many questions you asked but what was asked. By nature we learned to filter out that "non-important" information and group together minimal facts to come to a solution. However just because 5-why’s can be so easy to do, does not make it good or effective.

    People also prioritize to find that most important single why…. so which why is worse for a fire to occur: ignition cause, fumes cause, or excessive oxygen cause? Stop prioritizing too earlier in the game.

    Here is an example of decision bias and its impact on an aviation problem in ASQ Automotive Excellence. Read "Why ask why" here:

    Here is a root cause tip discussing "Common Sense" which is another skill needed to use 5-why’s.

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