fivewhys

Five Whys is a simple root cause analysis technique used to identify the underlying cause of a problem by repeatedly asking why. The approach aims to move beyond immediate symptoms to address fundamental processes that allow a defect or incident to occur. It is commonly used in lean manufacturing, quality improvement, and IT incident review.

Originating within the Toyota Production System, Five Whys is commonly attributed to Taiichi Ohno. It has since spread to many industries as a quick, inexpensive method for exploring cause-and-effect relationships. The core idea is that a sequence of questions about a problem can reveal a chain of causation, with each answer becoming the basis for the next why.

Process: Start with a clearly defined problem. Ask why the problem occurred and record the answer. If the answer points to a root cause, you may stop; if not, ask why again and repeat for several levels, often up to five. The goal is to uncover a root cause that can be corrected to prevent recurrence. Document the reasoning and propose corrective actions, then verify whether those actions address the root cause.

Strengths and limitations: Five Whys is fast, lightweight, and easy to learn, making it suitable for straightforward, single-cause problems. It can be biased by incomplete data or assumptions and may overlook multiple root causes. It is not a substitute for more formal analyses in complex systems and should be used with careful problem framing and evidence gathering. Variations exist, and the exact number of iterations is not fixed.