Five Whys (or 5 Whys): Root Cause Analysis for Problem Solving

The five whys (or 5 whys) in a nutshell:

Asking “Why?” five times is a technique to help you get to the root cause of a problem.

The Five Whys (or 5 Whys): A Root Cause Analysis for Better Problem Solving

Here’s a short 3-minute video introduction from Eric Ries, entrepreneur-in-residence at Harvard Business School:

“Behind every seemingly technical problem is actually a human problem waiting to be found.” — Eric Ries

The origin of the technique is typically attributed to Sakichi Toyoda and Taiichi Ohno at Toyota Motor Corporation:

“We come across problems in all sorts of situations in life, but, according to Taiichi Ohno, pioneer of the Toyota Production System in the 1950s, ‘Having no problems is the biggest problem of all.’ Ohno saw a problem not as a negative, but, in fact, as ‘a kaizen (continuous improvement) opportunity in disguise.’ Whenever one cropped up, he encouraged his staff to explore problems first-hand until the root causes were found. ‘Observe the production floor without preconceptions,’ he would advise. ‘Ask why five times about every matter.’“¹
“(The five whys method is) the basis of Toyota’s scientific approach by repeating why five times the nature of the problem as well as its solution becomes clear.”²

Here’s an easy five whys example to illustrate the idea²:

Problem: The vehicle will not start.

Why? – The battery is dead. (First why)
Why? – The alternator is not functioning. (Second why)
Why? – The alternator belt has broken. (Third why)
Why? – The alternator belt was well beyond its useful service life and not replaced. (Fourth why)
Why? – The vehicle was not maintained according to the recommended service schedule. (Fifth why, a root cause)