5 Whys
Concept
Toyota's Sakichi Toyoda popularized the 5 Whys: take any apparent cause and ask "Why?" five times in succession. Each answer becomes the new statement; you drill until you hit a root cause that isn't itself a symptom of something deeper.
In the consulting toolkit, 5 Whys complements issue trees. Issue trees go wide (every plausible cause). 5 Whys goes deep on one branch — the one you suspect dominates. It's especially useful after a Pareto step has named the vital 20%,
[Description truncada. Veja o README completo no GitHub.]