5 Whys: To get better, ask why.

If you have a 2-year-old, or remember one; you are familiar with the word “why.” Repeatedly. Now, here is a more adult way to use that word.

Lean tells us we should ask “why” all the time. In fact, the Five Whys to discover the root cause of a problem so we fix it once and for all.

Here’s how Taiichi Ohno explains it:

“It is difficult to do, even though it sounds easy. Suppose a machine stopped functioning:

1. Why did the machine stop?
   There was an overload and the fuse blew.
2. Why was there an overload?
   The bearing was not sufficiently lubricated.
3. Why was it not lubricated sufficiently?
   The lubrication pump was not pumping sufficiently.
4. Why was it not pumping sufficiently?
   The shaft of the pump was worn and rattling.
5. Why was the shaft worn out?
   There was no strainer attached and metal scrap got in.”

Repeating “why” five times, like this, can help uncover the root of the problem and correct it. The real cause is often hidden behind obvious symptoms.

Do you ask the Five Whys every time you have a bug in your software?

To hear further explanations from Taiichi Ohno, see Chapter 2 of his short book:

Toyota Production System: Beyond Large-Scale Production

There are many other great ideas in this book.

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