Theory of Five Whys

By Sameer Garg

The concept of 5 whys was first practised by Toyota as a tool for Root Cause Analysis. It is based on the “Cause and Effect ” theory. 

Any failure or problem faced in any system is not caused by visible reasons. Its roots lie elsewhere. 

It has been found that the Theory of 5 ‘whys’ helps in identifying the real cause of the problem and helps in eliminating the pain point permanently.

Nowadays, it’s also practised as a Root Cause Analysis tool and approached through fishbone diagrams. 

In auto manufacturing as a practice, the entire production line is stopped until such time the root cause of the problem is not detected. It may cause production losses in the short term but in the long term, it increases overall system efficiency by eliminating repetitive failures for the same reasons. 

To explain: If a car is not starting due to battery failure:

  1. First why: Why battery failed: Life of the battery was over and not replaced as due.
  2. Second Why: Why it was not replaced as due: Battery was not available in stock. 
  3. Third why: Why not available in the stock: Not delivered by the vendor in spite of timely order.
  4. Fourth Why: Why not delivered by vendor: Because his last bill was not paid.
  5. Fifth Why: Payment was made but the bank sent the payment in the wrong account.

The root of the problem can be traced to human error by banking partner.

As per experience, normally after 5 whys root cause is identified but it can be extended further depending upon the complexities of the problem.