5 Why

Getting to the root cause of a problem

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5 Why

The method finds the causes of a problem, and works out how the problem can be removed. Its great virtue is that it is simple.

Sakichi Toyoda introduced it, and it is part of the Toyota Production System. It is used all over the world.

When to use it

When what you want is the real, systemic cause of a problem that has happened recently.

When not to use it

When you still do not understand what exactly happened; see 5W+H.
When the problem has several different causes; see the Ishikawa diagram.

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