“Perhaps the most widely used technique at Amazon for these situations is the Correction of Errors (COE) process, based upon the “Five Whys” method developed at Toyota and used by many companies worldwide. When you see an anomaly, ask why it happened and iterate with another “Why?” until you get to the underlying factor that was the real culprit. This COE process requires the team who had a significant error or problem to write a document describing the problem or error, and to drill down on what caused it by asking and answering “Why?” five times in order to get to the true root cause.”