6 Five Whys

Toyoda also developed the concept of 5 Whys: When a problem occurs, ask “why” five times to try to find the source of the problem, then put into place something to prevent the problem from recurring. It is now a critical component of problem-solving training, delivered as part of the induction into the Toyota Production System.

The 5 Whys method is viewed 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.” Nowadays, the technique has reached other companies and organizations far beyond Toyota, and is now used within Kaizen, lean manufacturing, and Six Sigma.