Five Whys (Ohno)

Details
Full Name

Five Whys Root Cause Analysis

Core Concepts:

Iterative Causal Analysis

Ask "Why?" repeatedly (typically ~5 times) to drill down to root causes

Root Cause vs. Symptom

Distinguish between surface symptoms and underlying causes

Causal Chain

Each answer becomes the subject of the next "Why?" question

Actionable Root Cause

Continue until you reach a cause that can be acted upon

Simplicity

No complex tools or statistical analysis required

Team-Based Investigation

Collaborative exploration of causal relationships

Avoiding Blame

Focus on process failures, not individual fault

Countermeasure Identification

Once root cause is found, design interventions

Key Proponent

Taiichi Ohno (Toyota Production System, 1950s)

Historical Context

Core tool in Lean Manufacturing and Toyota Production System (TPS), foundational to continuous improvement (Kaizen)

When to Use:

  • Incident post-mortems in software/DevOps

  • Debugging when surface fixes don’t resolve the issue

  • Process improvement initiatives

  • Understanding recurring problems

  • Quality defect analysis

  • Any situation where symptoms are clear but causes are not

  • Kaizen (continuous improvement)

  • Root Cause Analysis (RCA)

  • Fishbone Diagram (Ishikawa) – complementary tool

  • A3 Problem Solving (Toyota)

  • DevOps post-mortem culture

Pitfall to Avoid:

  • Stopping too early at a symptom rather than root cause

  • Pursuing a single causal chain when multiple factors contribute (use Fishbone Diagram for complex causality)

  • Blame-focused questioning rather than system-focused

Example Application:

Problem: Website is down
Why? → Database connection failed
Why? → Connection pool exhausted
Why? → Long-running queries not timing out
Why? → No query timeout configured
Why? → Default configuration was never reviewed for production
Root Cause: Configuration review process missing
Countermeasure: Establish pre-production configuration checklist

Criticism:

  • Alan J. Card, "The problem with '5 whys'" (BMJ Quality & Safety, 2017) — no evidence of effectiveness despite wide institutional adoption; the technique pushes investigators down a single linear causal path and its results are not reproducible across teams

  • John Allspaw, "The Infinite Hows (or, the Dangers of the Five Whys)" (2014) — "why" questions invite blame and narrative bias in complex systems; he proposes asking "how" about the conditions instead

  • The deeper objection: in complex systems a single root cause often does not exist — incidents emerge from interacting contributing factors, which a five-step linear chain cannot represent