Five 5 Why Fallacies to Avoid

By Jon Miller Updated on November 8th, 2020

I was updating a few old articles on problem solving and came across some notes from a few years ago. These notes were on topics related to root cause analysis that I’ve written or spoken about. I picked out a few old favorites and packaged them here as five fallacies related to 5 why analysis. For more effective problem solving, avoid falling for these fallacies.

The Post Hoc Fallacy

Starting out with a bit of Latin, the post hoc fallacy is short for post hoc ergo propter hoc or “after this, therefore because of this”. It’s a mouth full in either language. This is a logical fallacy that problem solvers can fall into when we think, “Since event Y followed event X, event Y must have been caused by event X.” Since every time the rooster crows, the sun comes up, the sun must be summoned by the crow. There is correlation in that both thing happen in the morning, but there is no causation from the crow to the sun.

Our minds are always trying to make sense of the world, looking for meaning or reasons for situations and events. Perhaps in our evolutionary history, chances of survival were higher when we jumped to a conclusion and took action, rather than remained in place, contemplating cause and effect. Since tiger appeared after a rustling of the bamboo grove, tigers must be caused by rustling bamboo. This may sound silly, and is wrong in terms of cause-and-effect logic, but it’s not terrible heuristic. The downside to following it is low, and the one time that Y does follow X, we avoid ending up in the tiger’s belly.

The way to avoid this fallacy when practicing 5 why analysis is to apply the “therefore” test. If we said “a tiger appeared because the bamboo rustled” then we try out “the bamboo rustles, therefore a tiger appears”. This hypothesis could be easily tested. Shake a handful of the vegetation and observe that this produces no tiger.

The 5 Why Fill-in-the-Blank Fallacy

Modern management often requires justification for investment of time or money. This is the responsible thing to do, whether with our personal resources or those entrusted to us by others. One of the challenges with Lean is that traditional approaches to accounting, budgeting and justifying investment don’t always encourage good decisions.

A common example of this is tying quarterly goals to Lean training or Lean transformation activities. Lasting results may take multiple quarters of effort, while efforts focused on immediate results often fail to sustain. Another example is requiring ROI calculation for valuable Lean efforts that organizations either can’t or don’t measure, such as morale, trust or autonomy. Along this same well-intentioned line of thinking is the “no solution without a 5 why analysis” policy, which often leads to the fill-in-the-blank fallacy.

I’ve seen this happen when teams are encouraged to do problem solving, but instead of receiving kata-style coaching to develop their thinking, they are told to fill out an A3 report. The intent of having everyone follow a common problem solving process, clarify the problem, and document root cause analysis is good. But without coaching, the resulting behavior can be fill-in-the blank compliance. In the worst cases, people just summarize what they’ve already decided to do, listing justifications in the root cause section.

The Five Options Fallacy

In Japan, the term “5 why” is not common. There, this process is called “Why-Why”. This doesn’t mean two times why; it means repeated whys. In many languages, repeating a word twice modifies its meaning. In the case of why-why it is continuation and intensification. This is less common in English, but it’s similar to saying “the drip drip of a faucet” to indicate that it’s steadily dropping, rather than to say it dripped twice.

Really, we should get away from the number five altogether when talking about why analysis, but it’s an easy handle to grab onto. At the very least, we should avoid the five options fallacy. This is when we treat 5 why as “the top 5”.  We may think that if we identify the top 5 causes, and come up with the 5 best ideas, we can solve a problem. Unfortunately, the defeats the whole point of five why, which is to go deep into the heart of the problem.

Eric Ries introduced the term Lean and many of its concepts including 5 why to a broad new audience in his book The Lean Startup. The book presented 5 why in the form of the five options fallacy. It represented 5 why analysis as asking five different why questions related to a problem or market need. While pursuing five separate options simultaneously makes sense when testing out new ideas, starting a new business or even problem solving, it’s not what five why root cause is about.

Exactly Five Fallacy

Why five? The name came about because, as the story goes, someone approached Taiichi Ohno trying to sound smart and asked, “Shouldn’t we use the 5W1H approach here?” and Ohno said, “You don’t need all of that. Just ask why five times.”

It’s important to understand the context of the problem in terms of who, what, where, when, and how. Working on the right problem, clarified, stratified and properly broken down, is key to effective continuous improvement. But these things come a few steps prior to the root cause analysis in the practical problem solving cycle.

Three is the magic number. Seven is the lucky number. Five falls at their midpoint. We have five fingers. We have the high five, the gimme five and the take five. But five alive, there’s no rational reason for that number in 5 why analysis. We certainly shouldn’t stop at five when investigating root causes.

The Anchor Tool Fallacy

This fallacy is less about the 5 why and more about trying to oversimplify one’s approach to continuous improvement by picking one tool, template, activity etc. for everyone to learn and use. It may be a commonsense approach if the tool happens to suit most or all people and situations. It may be true that it’s easier to get buy-in to learn and try one tool rather than two or more. But when it comes to the business of rooting out causes of complex problems, too often anchoring on 5 why or any one tool fails to lead us from ignorance to insight. In reality, there are a handful of root cause analysis tools that work very well when used together correctly.

The form of the tool less important than its purpose. In the case of 5 why, the purpose is to get to an actionable root cause. Taking action on a root cause involves a chain of events from detecting the problem, identifying its source, coming up with and seeing countermeasures through, and monitoring and controlling the process afterwards. Strengthening only one part of this chain is rarely enough.

I’ve seen organizations whose people struggled because leadership framed problems in the wrong way. I’ve seen organizations that relied too much on go see and intuitive action and others too much on cautious data analysis. In these cases, it was a lack of self-awareness and not an inability to ask the 5 whys that held them back.

Drawing General Insights from the 5 Why Fallacies

Hopefully you’ve seen by now that we arrived at the number in 5 why analysis in an arbitrary way. Moreover, I’ve argued that the choice of the English word “why?” itself is arbitrary, or at the least not an ideal fit. I’ve argued for asking “how?” or “how come?” or “how did it come to pass?” as better ways to untangle cause-and-effect than “why?”

There are general insights to be drawn from all of this. That is, when learning an accepted or established method, we should question its origin, its intent, its received form, and how this may have deviated from the source. Doing these things allows us to be aware of fallacies and pitfalls that result from taking accepted norms at face value.

The number of fallacies in this list is also arbitrary. What other five why fallacies have you encountered?

  1. Mike Osterling

    November 9, 2020 - 1:06 pm

    Another wonderful article Jon – thanks. Another fallacy I commonly see is the expectation that there is only one answer to the question “why.” Often there are multiple causes, or causes that only occur in conjunction with another factor / cause (the bad thing happens only if two things occur – I was given a speeding ticket because I was driving over the speed limit, AND it was witnessed by a law enforcement officer)

    • Jon Miller

      November 9, 2020 - 5:20 pm

      Hi Mike. Great addition to the list. Thanks for the comment!

  2. Rob van Stekelenborg

    November 11, 2020 - 10:34 am

    Common issues with “why-why” analysis that I typically come across:
    1. Teams start with a generalized problem, not a concrete, specific instance. This leads to generalizations.
    2. Lack of recency. This leads to guesses.
    3. Externalization of the source of the problem. It’s always the supplier, customer, manager, system, or colleague…
    4. Trivialization of the problem leading to jumping to a quick fic (an often known “solution”).
    5. Accusations and blame which blocks the analysis and makes it personal.
    6. Excuses instead of causes. You can hear this when people answer that it happened to prevent something else from happening.
    7. No logic nor evidence of the causal relationship between question and answer. Lack of testing.
    8. No link between the questioning sequence and the “mechanics” of the system (either the equipment or the steps in the process).
    I wrote an earlier post about the above pitfalls of “why-why” that you can read here if interested: https://dumontis.com/2011/06/5xwhy/

    • Jon Miller

      November 13, 2020 - 1:37 am

      Solid contribution to the list! Thanks for sharing your insights Rob

  3. Jenna Robinson

    November 18, 2020 - 7:14 pm

    Great article! I am currently working on my Green belt project and figuring out our 5 whys. The main issue our group came across was that there are way more than just 5 “whys”. In order to truly get to the root cause of a problem, we need to ask many question. Your paragraph about the Five Options Fallacy was especially interesting because it points out the importance of not just asking 5 whys. I think the why-why statement Japan uses really exemplifies that point.

    • Jon Miller

      November 18, 2020 - 8:46 pm

      Thanks for your comment Jenna. It’s great to hear that you are learning this lesson hands on. The earlier the better!

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