6. 5 whys

Sakichi Toyoda would have designed the Lean system of the "five whys". It is one of the significant approaches that Toyota uses to solve problems. The theory is to evaluate the problem before the root cause or causes are found, not to stop at the first cause of a problem (the first why). In fact, it is more of a theory than a cause analysis tool since it is not sufficiently organized nor 'accurate' (why 5 and not 4, 6? In the 2nd, the root cause can be quite well discovered) [44].
