The 5 Whys simply requires that the user ask "why?" several times over. The technique is called the "5 Whys" because it is the experience of its inventor, the Toyota company, that "why" needs to be asked successively five times before the root cause is established.

This simple but very effective technique really amounts to a questioning attitude. Never accept the first reason given; always probe behind the answer. It goes along with the philosophy that a defect or problem is something precious; not to be wasted by merely solving it, but taking full benefit by exposing the underlying causes that have led to it in the first place. Many believe that it is this unrelenting seeking out of root causes that have given the Japanese motor industry the edge on quality, reliability and productivity.

An example follows: A door does not appear to close as well as it should. Why? Because the alignment is not perfect. Why? Because the hinges are not always located in exactly the right place. Why? Because, although the robot that locates the hinge has high consistency, the frame onto which it is fixed is not always resting in exactly the same place. Why? Because the overall unit containing the frame is not stiff enough. Why? Because stiffness of the unit during manufacture does not appear to have been fully accounted for. So the real solution is to look at the redesign of the unit for manufacture.

Perhaps there are even more Whys. Why did this happen in the first place? (Insufficient co-operation between design and manufacturing.) Why so? (It was a rushed priority.) Why? (Marketing had not given sufficient notice.) Why? And so on.

The 5 why analysis gives guidance to the role of an effective quality department. With total quality established, much responsibility for quality will be placed "at source", that is with the person that makes it. But this is not sufficient. The quality professionals need to be spending more time on the detective work of tracing problems to their root cause. This is real continuous improvement and prevention.

A variation of the 5 Why technique is the "5 How" technique. This is often used in tracing the cause of a failure in a product or in service delivery. ("How did that happen?"....) The thinking and procedure is exactly the same.