Teruyuki Minoura (Toyota Exec) Talks About Problems with 5-Whys
The following is quoted from a Toyota website that has more recently been removed. A Toyota Exec is talking about the Toyota Production System.
The article says:
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When an error occurs, the first thing that needs to be done is fix the error. Minoura recalls that Ohno used to order them to ask the question “Why?” five times over because “that way you’ll find the root cause, and if you get rid of that it’ll never happen again.” However, Minoura emphasizes that on-the-spot observation rather than deduction is the only correct way to answer a “Why?” question. “I’m always struck that the five-why method doesn’t seem to be working as well as it should be because there’s been a lack of practical training. The reason is that they end up falling back on deduction. Yes, deduction. So when I ask them ‘Why?’ they reel off five causes as quick as a flash by deduction. Then I ask them five whys again for each of the causes they came up with. The result is that they start falling back on deduction again, and so many causes come back that you end up totally confused as to which of them is important.”
“Through real training,” Minoura says, “you’ll be able to discover dozens of problems and also get to their root causes. You’ll be able to make dozens of improvements. If you incorporate all the accumulated knowledge of root causes that you’ve got from always asking ‘Why? Why? Why? …’ into your equipment, you’re going to have something that no one else can come close to. I don’t think it’s got anything to do with nationality; it all has to do with whether or not you’ve received the proper training. I feel though that the tendency to give that kind of training and education forms the basis of Toyota’s approach to monozukuri.”
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Most people that talk to me about 5-Why’s, Cause-and-Effect, or Fault Trees stress the need for deductive reasoning to find root causes. Yet here is someone who worked under Ohno (the 5-Whys expert) who says that deduction is BAD – only direct observation is good.
I like the idea of direct observation. But I think people need more guidance than just asking “Why” 5 times to be able to solve difficult problems. Perhaps 5-Whys works for a simple problem. But how do you know if a problem is simple before you solve it?
Maybe 5-Why’s would work for a dedicated master problem solver like Ohno. But it is difficult – or perhaps impossible – to train everyone needed to his level of skill.
That’s why in the TapRooT® System for Root Cause Analysis, we’ve built an expert system to help people find the root causes of human performance and equipment problems. This helps everyone – from the novice problem solver to the expert – perform better root cause analysis.
And we teach people to use direct observation – the facts – to find root causes using a root cause analysis tool called the Root Cause Tree® Diagram.