Evolution of the Toyota Production System

Repeating Why Five Times

WHEN CONFRONTED WITH a problem, have you ever stopped and asked why five times? It is difficult to do even though it sounds easy. For example, 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 ...

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