Lean Manufacturing in Simple Terms: 5 Why's

There are several established failure analysis methods that have been proven to be effective in the manufacturing world. "Fish bone" analyses and cause-and-effect diagrams are examples of two widely used tools for discovering what is wrong in a particular situation, such that a corrective action can be taken. In many cases, however, these take time and energy to put together. Perhaps a simpler approach, such as the 5 Why's method, would help to find the source of a problem a little quicker, possibly avoiding the need for other research-intensive efforts. The 5 Why's method, a recognized lean manufacturing technique, challenges those working an issue to peel back the layers of a problematic situation one at a time, hopefully exposing a root cause that can be corrected.

5 Why's - What is it? If you are a parent, you will recognize the fact that most children use this method on a frequent basis, partially out of natural curiosity, and partially to drive a parent nuts.

"Dad, why can't I have my dessert?"

"Because you didn't eat your vegetables."

"Why do I have to eat my vegetables?"

"So you'll have a strong body and not get sick."

"Why do vegetables help me stay strong?"

Usually, at this point, when it seems that the "why's" could go on forever, the parent will tire of the process or not have an understandable answer, in which case, the conversation is closed with, "Because I said so!"

As silly as it sounds, though, the child is following a very simple problem-solving approach. Ask a question about an issue. Get an answer. Ask a second question as to why the previous answer is true. Get another answer. Ask "why" a third time, and a fourth time, etc. The point is, if you ask "why" enough times, eventually you may find the root cause of the problem, and be able to address it with a corrective action.

In the lean manufacturing world, where systematic problem-solving is required to reduce the number of substandard products from a factory, the 5 Why's method should be used first to see if there is a simple answer for a tough issue.

Why were last month's sales so low?

Because our main customer wasn't satisfied with his last shipment of green widgets.

Why wasn't he satisfied?

Because they were slightly smaller than the last shipment he received from us.

Why were they smaller?

Because we accidentally used an old obsolete drawing to build the parts.

Why did we mistakenly use the wrong drawing?

Because we have a new production engineer that didn't know the difference.

Why wasn't he trained to know what was correct?

Because we've stopped using the training manual for new employees.

Why....and so on, and so on.

In this case, the 5 Why's method may finally point to a process problem, a flawed company policy or practice, or something that has changed in the recent past.

As one can see, there is nothing magic about the number 5. A solid conclusion could be reached after only three or four iterations, or it may take ten. The name of the 5 Why's method merely suggests that "why" should be asked enough times that nothing is taken for granted in examining the issue.

The 5 Why's approach may not always reveal the true cause of a problem without additional research and supplemental data. At some point in the process, the answer to a "why" question may require someone to go look at trend data or see if there has been some minor undetected change in the process. But, a problem-solving team using the 5 Why's method may uncover things that need to be looked at further. The 5 Why's approach can help the team establish priorities for the follow-up research based on which items are the most likely causes.