Root Cause Analysis

When engineers do a failure investigation one of the tools we us is called Root Cause Analysis. The idea is to get to the ultimate reason for the failure. One of the techniques used is called "The 5 Whys." You keep asking "why" until you cannot go any further. Usually about 5 times will do it. Here's an example of the 5 whys in practice.

In the mid-70's I was living in Japan as one of the owners representatives for new construction in a Japanese shipyard. I worked with an older Japanese gentleman who we shall call Ishimoto. Ishimoto was a pilot during the war and had a bad back. One day I asked, "Ishimoto-san, how did you hurt your back?"
"Plane crash" was the answer.
"Why did your plane crash?" I asked.
"Run out of gas." he replied.
"Why did you run out of gas?"
"American shoot holes in gas tank!"

And so we come to the root cause of Ishimoto's bad back.