5Why

Five Whys is a simple root cause analysis method used to identify the underlying reasons behind a problem by repeatedly asking the question "Why?". The technique aims to move beyond symptoms to reveal the causal chain that leads to the issue, often stopping after five iterations, though the number is not fixed.

The basic process involves defining the problem clearly, then asking why it occurred and recording the answer. If the answer is not the root cause, the question is asked again with respect to the new information. This iterative questioning continues until a likely root cause is identified or no further meaningful why questions can be asked. After determining a root cause, corrective actions are proposed and tested to verify that the fix prevents recurrence.

Origins and use have strong ties to Toyota and the broader lean manufacturing movement. The method is commonly attributed to Sakichi Toyoda and was popularized in the Toyota Production System, where it was used to analyze quality and process failures. Today, Five Whys is applied across industries including manufacturing, software development, healthcare, and service operations as a lightweight tool for problem solving and continuous improvement.

Advantages of the Five Whys include its simplicity, minimal data requirements, and rapid insight, making it accessible to cross-functional teams. Limitations include the potential for oversimplification, reliance on the investigator’s knowledge, and the risk of stopping at an incorrect root cause if the questions are poorly framed. It is often used in conjunction with other tools, such as fishbone diagrams or data analysis, to provide a more robust investigation.