Management & Thinking
Pro5 Whys
5 Whys 五問追因 · Source: Sakichi Toyoda · Toyota Production System
Incidents, bugs, customer complaints, team friction — any problem you want to trace to root cause, not stop at surface symptom
Core Concept
Invented by Sakichi Toyoda, central to the Toyota Production System: ask "why" five times about a problem, each answer becomes the target of the next "why." Designed to cut through symptom-layer, behavior-layer, and process-layer to reach where you can actually fix things — usually a system design flaw, not "someone wasn't paying attention." Common failures: asking five "whos" (witch-hunt), stopping at layer 2–3 (still symptom), answering with opinion rather than fact. Five is a convention; the real target is reaching a layer you can change.
Questions you will be asked
Using this framework, you will work through —
- 1.Describe what happened. Facts, not evaluations.
- 2.Why 1: Why did this happen?
- 3.Why 2: Why did the previous cause occur?
- …and 3 more