Definition
A simple problem-analysis method that asks "why" five times in a row to close in on the root cause. Limitations: time-consuming, results are not reproducible across teams, does not guarantee finding the true cause, and the outcome depends on the quality of the questions asked.
In detail
The Five Whys (5 Whys) is a simple problem analysis method that approaches the Root Cause of a problem by repeatedly asking "why." It is usually used in daily problem solving and Kaizen activities to help teams move from surface symptoms down to the root at the system or process level. Compared with tools such as the Cause and Effect Diagram, it is faster and more focused, but the result depends on the questioner's experience and knowledge, and different teams may reach different conclusions. When using it, note its limitations: it is time-consuming, results are not repeatable, it does not guarantee finding the true cause, and it depends on the quality of the questions. Its output is usually a Root Cause statement that provides the basis for developing Countermeasures.
Example in practice
Scratches appear on a batch of products on the production line. The team leader gathers employees and continuously asks why: Why are there scratches? Because there is foreign matter on the conveyor belt; why is there foreign matter? Because cleaning is not thorough; why is cleaning not thorough? Because the cleaning standard is not clear; why is the standard not clear? Because after a changeover, no one is responsible for updating the cleaning standard; why is no one responsible? Because that maintenance responsibility was never assigned to any role after a changeover. The countermeasure lands on naming an owner for the standard and building a process to keep it updated.