5 Whys

The '5 Whys' is a technique originally developed by Sakichi Toyoda. It was later used as "the basis of Toyota's scientific approach… by repeating why five times, the nature of the problem as well as its solution becomes clear."

5 Whys

Reasons that the 5 Whys system may not always be successful include:

  • Tendency for investigators to stop at symptoms rather than going on to lower-level root causes.
  • Inability to go beyond the investigator's current knowledge, therefore they cannot find causes that they do not already know.
  • Lack of support to help the investigator ask the right "why" questions.
  • The use of the 5 Whys as a stand-alone tool, without using the preparation and preliminary phases mentioned.
  • Investigation stopped at the 5th "why", even though more questions could/should be asked.
  • Results may not always be repeatable – different people using the 5 Whys may come up with different causes for the same problem.
  • Tendency to isolate a single root cause, whereas each question could elicit many different root causes.
  • The output from the use of the 5 Whys tool can lack forms of verification to prove its correctness.