Five Whys

Overview

The Five Whys is a root-cause analysis technique developed by Taiichi Ohno at Toyota. You start with a visible symptom and ask "Why did this happen?" repeatedly — each answer becomes the subject of the next question — until you reach the systemic cause rather than stopping at the proximate one.

Problem (symptom)
  └─ Why? → Cause 1
       └─ Why? → Cause 2
            └─ Why? → Cause 3
                 └─ Why? → Cause 4
                      └─ Why? → ROOT CAUSE (act here)

Five is a guideline, not a rule. Stop when you reach a cause that is actionable and where fixing it would prevent recurrence.

Core Concepts

Symptom vs. Root Cause

The symptom is what you observe; the root cause is the condition that made the symptom inevitable. Fixing a symptom stops this instance; fixing the root cause prevents the class of problem.

The Causal Chain

Each why step must be a direct cause of the step above it — not a parallel factor, not a contributing influence. If you can ask "but also why?" and get a different chain, you may have a branching problem requiring a fishbone diagram instead.

Actionability

A valid root cause must be something a person or team can actually change. "The system is complex" is not actionable. "No one owns monitoring for this service" is.

The "Five" Number

Ohno chose five because most surface-level explanations exhaust themselves in 2–3 whys; the 4th and 5th force you past the obvious. In practice, chains run 3–7 steps depending on domain.

How to Apply

Step 1 — Write a precise problem statement

Do not start with vague language. Bad: "the deployment broke." Good: "The production deployment at 14:32 UTC caused a 23-minute outage for all EU users." Ambiguous problem statements produce ambiguous root causes.

Step 2 — Ask the first "Why?"

What directly caused the problem statement to be true? Write it down. This should be a fact, not a guess — verify with data, logs, or direct observation if needed.

Step 3 — Continue asking "Why?" for each answer

Take the answer from the previous step and ask why that is true. Do not skip levels or jump to conclusions. Each step must follow logically from the one above.

Step 4 — Test the chain by reading it back

Read the chain bottom-up using "therefore": "We have no alerting policy, therefore the disk filled silently, therefore the database stopped writing, therefore the API returned 500s, therefore users saw outage." If any link breaks, the chain is wrong — revise.

Step 5 — Define a corrective action at the root

Assign an owner, a deadline, and a success metric. A root cause without an owner is not actionable. Also consider whether earlier links in the chain warrant secondary fixes to reduce blast radius.

Output Format

╔══════════════════════════════════════════════════════════════════════════════════╗
║                           FIVE WHYS ANALYSIS                                    ║
╠══════════════════════════════════════════════════════════════════════════════════╣
║  PROBLEM  │ [precise description of symptom — what, when, who was affected]     ║
╚═══════════╧══════════════════════════════════════════════════════════════════════╝

  ┌─────────────────────────────────────────────────────────────────────────────┐
  │  SYMPTOM  ►  [problem restatement]                                          │
  └───────────────────────────────────┬─────────────────────────────────────────┘
                                      │ Why?
                                      ▼
  ┌─────────────────────────────────────────────────────────────────────────────┐
  │  WHY 1    ►  [direct cause of the problem]                                  │
  └───────────────────────────────────┬─────────────────────────────────────────┘
                                      │ Why?
                                      ▼
  ┌─────────────────────────────────────────────────────────────────────────────┐
  │  WHY 2    ►  [cause of Why 1]                                               │
  └───────────────────────────────────┬─────────────────────────────────────────┘
                                      │ Why?
                                      ▼
  ┌─────────────────────────────────────────────────────────────────────────────┐
  │  WHY 3    ►  [cause of Why 2]                                               │
  └───────────────────────────────────┬─────────────────────────────────────────┘
                                      │ Why?
                                      ▼
  ┌─────────────────────────────────────────────────────────────────────────────┐
  │  WHY 4    ►  [cause of Why 3]                                               │
  └───────────────────────────────────┬─────────────────────────────────────────┘
                                      │ Why?
                                      ▼
  ╔═════════════════════════════════════════════════════════════════════════════╗
  ║  ROOT     ►  [cause of Why 4 — the systemic condition to fix]              ║
  ║  CAUSE       ● act here                                                     ║
  ╚═════════════════════════════════════════════════════════════════════════════╝

┌──────────────────────────────────┬──────────────────────────────────────────────┐
│         ROOT CAUSE SUMMARY       │             CORRECTIVE ACTION                │
├──────────────────────────────────┼───────────┬──────────────┬───────────────────┤
│ [restate root cause in one clear │  What     │  Owner       │  Due    │  Metric │
│  sentence]                       ├───────────┼──────────────┼─────────┼─────────┤
│                                  │ [change]  │ [person/team]│ [date]  │ [signal]│
└──────────────────────────────────┴───────────┴──────────────┴─────────┴─────────┘

  Secondary Actions (optional):
  ├─ Why N level ►  [fix to reduce blast radius at an intermediate link]
  └─ Why N level ►  [additional hardening action]

Each row in the causal chain must be a direct cause of the row above it — read the chain bottom-up with "therefore" to verify every link holds. The Root Cause box marks the single point where a corrective action will prevent recurrence; Secondary Actions address intermediate links to limit blast radius if the root fix is delayed.

Common Mistakes

• Stopping too early. Why 1 or Why 2 is almost always a symptom, not a cause. "The server crashed" is not a root cause. Keep going until you hit a process, policy, or ownership gap.
• Asking "Who?" instead of "Why?" Five Whys is a process analysis tool, not a blame tool. The moment a chain ends with a person's name, redirect to "Why was that person in a position to cause this?" or "Why did the process allow this?"
• Branching silently. If there are two independent causes for a why step, document both chains separately — do not merge them. Hidden branches produce fixes that only address half the problem.
• Confusing correlation with causation. "The outage happened on Friday" is not a cause. Each step must be a direct causal mechanism, not a correlation.
• No action assigned. A completed Five Whys with no owner and deadline is a discussion artifact, not a corrective action. The analysis is only complete when someone is accountable for the fix.
• Applying it to novel or complex systems alone. Five Whys works well for repeatable, understood processes. For novel failures in complex systems, pair it with a timeline reconstruction or fishbone diagram to surface all contributing factors first.

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