Five Whys

Definitions

1. A root cause analysis technique where you ask 'why?' five times to drill down from a symptom to its underlying cause. Why did the server crash? Memory leak. Why the leak? Unclosed connections. Why unclosed? Missing error handler. Why missing? No tests. Why no tests? Culture doesn't prioritize them.

   In plain English: A problem-solving trick where you keep asking 'why did that happen?' five times in a row to dig past the surface symptoms and find the real root cause.

2. Developed at Toyota as part of the Toyota Production System, the Five Whys works best for simple causal chains. For complex system failures with multiple contributing factors, techniques like the Ishikawa (fishbone) diagram or formal incident analysis provide more thorough investigation.

   Example: 'The Five Whys told us the root cause was missing input validation. But the real question is: why does our development process allow unvalidated inputs to reach production?'

   Source: Toyota / limitations

Related Terms

• Rubber Duck Debugging
• Postmortem
• Rubber Duck Conference
• Root Cause Analysis
• Blameless Postmortem
• Five Whys
• Waterfall Culture