The 5 Whys is a root-cause analysis technique developed by Sakichi Toyoda and refined within the Toyota Production System. By repeatedly asking "Why?" — typically five times — you move from surface-level symptoms to the underlying cause of a problem. Simple, fast, and remarkably effective for operational and interpersonal problems, it is the most widely-used structured problem-solving technique in manufacturing, software, and management worldwide.
Root Cause Analysis (RCA) is a systematic process for identifying the fundamental causes of problems — not just their symptoms — so that interventions prevent recurrence rather than merely resolving the immediate incident. Developed in industrial safety and quality management, RCA has become standard practice in healthcare, software engineering, aviation, and organisational management for post-incident learning.
The Theory of Constraints (TOC), developed by Eli Goldratt, holds that every system has exactly one constraint — a bottleneck — that limits its overall throughput. Identifying and eliminating that constraint (then finding the next one) is the highest-leverage action available. TOC provides a complete methodology for diagnosing and systematically improving the throughput of any complex system, from manufacturing to software development to organizational performance.