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Five Whys


A method called Five Why is popular among Lean. Many focus on formats, and some focus on the quantity of whys.


Taiichi Ohno’s “Toyota Product System” has this chapter about the Five Whys. The chapter starts with the following;


“When confronted with a problem, …”


Ohno, Taiichi. Toyota Production System: Beyond Large-Scale Production (p. 17). Taylor and Francis. Kindle Edition.


The original Japanese version does not start with a “problem.” Ohno uses the word Jishou【事象】.


“Jishou” is a bit complicated word. It can be translated as a phenomenon. Ohno’s first sentence starts with “When confronted with one phenomenon.” But the phenomenon has another word to translate in Japanese, which is Genshou【現象】. What is the difference between the two?


Genshou 【現象】 can be said for every phenomenon which humans can perceive. The first symbol 【現】 means appear or now. It is one of the symbols of Genba【現場】. It is used for broad phenomenon.


Jishou 【事象】 is used as a phenomenon that appeared under certain circumstances. In other words, it is happening under limited conditions or narrow scope.


Jishou is also a mathematics word. It is used in probability and is the translation of “event.” It is essential to understand the Jishou as a mathematical “event.” Ohno suggests applying the Five Whys to “one event.” Defining this “one event” is crucial. It represents one takt time or each unit. Intervals such as monthly, weekly, daily, or hourly are collections of events.


Understanding the difference between the two helps us correctly use the Five Whys.


In a plant, someone was working on a problem. The problem statement was “missing material.” 😣 That is a huge problem or a general phenomenon. We need to state the phenomenon in more limited conditions.

“When did this happen?”

“Where did this happen?”

“What was missing?”

“Who found the problem?”

These questions are critical to limit the phenomenon to be more specific. And ask the Five Whys to each of these particular problems.


So, how should we approach general phenomenon?


“To tell the truth, the Toyota production system has been built on the practice and evolution of this scientific approach.”


Ohno, Taiichi. Toyota Production System: Beyond Large-Scale Production (p. 17). Taylor and Francis. Kindle Edition.


The original word that was used for the “practice” is “Ruiseki”【累積】. The correct translation for “Ruiseki” is accumulation. Or another proper word will be piled up. As we do many Five Whys, we should have an accumulation or pile of those works. One of my coaches always asked where is the pile of problem-solving? He hated the statistics of problems and selecting top whatever issues. “When you have so many problems, why do you limit the quantity of problem-solving?”


The original word that was used for the “evolution” is “Tenkai”【展開】. The correct translation for “Tenkai” is deployment or expansion. There is a word called “Yokoten,” which initially meant horizontal deployment. When we conduct one Five Whys analysis, we shouldn’t satisfied with that. We should seek similar problems until we reach a general phenomenon.


And Ohno explains how he came up with “Jidouka,” “Heijyunka,” “Kanban,” and “Profits and motivation” in the following paragraphs. His answers are all to general problems, such as “low productivity” or “over-production.” Ohno is saying that by accumulating and deploying the Five Whys on specific "events," he reached solutions to more general problems.


And the essence of reaching that general problem is “self-questioning.” Ohno has repeatedly used in this chapter, and not translated, a word 【自問自答】, which is translated as “self-questioning.” But I would be careful. If I translate symbol by symbol this will be Self-Question-Self-Answer. It is a mindset of asking questions about things you aren’t convinced of. It’s the state of continuous questioning. What is important here isn’t just about getting the answers. But coming up with the right question. Because when you ask the wrong question, you will come up with the wrong answer.


So, don’t ask vague questions to start a Five Whys analysis. Don't get satisfied just because you did one. Accumulate and expand them. And only those who can continue self-questioning and answering can reach a solution to broader problems.


The final paragraph of this chapter about Five Whys is analyzed in depth here.

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