Full definition
Root cause analysis technique that asks "why?" repeatedly (typically 5 times) until reaching the fundamental cause of a problem. Example: bearing fails → why? insufficient lubrication → why? wrong lubrication interval → why? maintenance plan not updated. Developed by Sakichi Toyoda, adopted in Toyota Production System and Six Sigma. Simple, requires no software. Limitation: may surface multiple causes; complement with Ishikawa diagram for complex problems.