The 5 Whys was developed as a root cause analysis technique in the 1930s by the founder of Toyota Industries, Sakichi Toyoda. Where it is suspected that there are multiple root causes, asking ‘Why?’ repeatedly can uncover those causes. Whether or not the 5 Whys needs to be implemented formally, simply questioning everything relating to an intractable problem – almost as a stream of consciousness exercise – can uncover hitherto unseen root causes and related issues.
5 Whys is also used as a tool at the Analyse phase of the process improvement methodology Six Sigma. The technique is best used by those who work day by day with the process that is being examined.