Five Whys

Definition
Systematically asking why an event occurs or a condition exists. The question "why?" is applied to each response until the root cause of the event or condition is found. Sometimes the root cause is identified by the 2nd or 3rd "why." In other situations it may take 6-7 "why's" to get to the root cause. Try to get to the 5th level without getting to an absurd level of detail.

At the heart of this simple tool is the belief that real problem solving occurs when the cause, rather than the symptom, of the problem is addressed. This is often referred to as "drilling down" to the heart of the problem. Dr. Kano refers to this "drilling down" as "going an inch wide and a mile deep into a problem" (real understanding leading to targeted solutions) rather than "going a mile wide and an inch deep into a problem" (superficial understanding leading to shotgun solutions). At a more philosophical level, the 5 Why's also demonstrate Dr. Deming's principle that the real problem usually lies in the deeper system rather than in the performance of an individual who is working within that system.