five-whys（五个为什么）

Five Whys - Root Cause Analysis

Systematic guide to uncovering root causes through iterative questioning, originally developed by Sakichi Toyoda for Toyota Motor Corporation.

When to Use This Skill

• Investigating recurring problems
• Debugging system failures
• Understanding customer churn
• Analyzing project delays or budget overruns
• Post-mortem analysis
• Process improvement initiatives

Core Concepts

The Method

Problem Statement
    ↓
Why? → Answer 1
    ↓
Why? → Answer 2
    ↓
Why? → Answer 3
    ↓
Why? → Answer 4
    ↓
Why? → Answer 5
    ↓
Root Cause Identified
    ↓
Solution Implementation

Key Principles

Questioning Techniques

Standard Approach

For each iteration, ask:

• Why did this happen?
• What caused this situation?
• What led to this outcome?

Alternative Phrasing (Less Confrontational)

When direct "why" questions feel threatening, use softer alternatives:

Root Cause Investigation

Understanding Motivation

Understanding Decisions

Analysis Framework

Step 1: Define the Problem

Be specific and measurable:

❌ Bad:  "The system is slow"
✅ Good: "Page load time increased from 2s to 8s after the March release"

❌ Bad:  "Customers are unhappy"
✅ Good: "Customer churn increased by 40% over three months"

Step 2: Iterate Through Whys

Document each level clearly:

Problem: Customer churn increased by 40%

1. Why? → Customers canceling after free trial
2. Why? → Not seeing enough value during trial
3. Why? → Not completing the onboarding process
4. Why? → Onboarding too complex, requires too much setup
5. Why? → Product lacks automation and intelligent defaults

Root Cause: Poor onboarding experience due to lack of automation

Step 3: Identify Solutions

Target the root cause, not symptoms:

Symptom-level fix (avoid):
├── Offer discounts to retain customers
└── Send more reminder emails

Root cause fix (preferred):
├── Build automated data import
├── Create intelligent defaults by industry
├── Simplify onboarding to 3 steps
└── Add progress indicators

Output Template

After completing analysis, document as:

## Five Whys Analysis

**Problem Statement:** [Clear, measurable problem description]

**Analysis Date:** [Date]

**Participants:** [Who was involved]

### Question Chain

1. **Why?** [First answer with evidence]
2. **Why?** [Second answer with evidence]
3. **Why?** [Third answer with evidence]
4. **Why?** [Fourth answer with evidence]
5. **Why?** [Fifth answer with evidence]

### Root Cause

[Identified root cause - the systemic issue to address]

### Recommended Solutions

| Priority | Solution     | Expected Impact | Effort   |
| -------- | ------------ | --------------- | -------- |
| High     | [Solution 1] | [Impact]        | [Effort] |
| Medium   | [Solution 2] | [Impact]        | [Effort] |
| Low      | [Solution 3] | [Impact]        | [Effort] |

### Success Metrics

- [How will we measure if the solution worked?]

Classic Examples

Manufacturing Example (Toyota Original)

Problem: Machine stopped operating

1. Why? → Motor overheated
2. Why? → Wasn't lubricated enough
3. Why? → Oil pump failed
4. Why? → Filter was clogged
5. Why? → No regular maintenance schedule

Root Cause: Lack of preventive maintenance procedures
Solution: Implement maintenance schedule and checklist

SaaS Example

Problem: Customer churn increased 40%

1. Why? → Customers canceling after free trial
2. Why? → Not seeing enough value during trial
3. Why? → Not completing onboarding
4. Why? → Onboarding too complex
5. Why? → Lacks automation and smart defaults

Root Cause: Poor onboarding experience
Solutions:
- Automated data import from popular tools
- Intelligent defaults based on industry
- Simplified 3-step onboarding
- In-app progress indicators

Result: 60% decrease in churn, 35% increase in trial conversion

Software Bug Example

Problem: Production API returning 500 errors

1. Why? → Database queries timing out
2. Why? → Query taking 30+ seconds
3. Why? → Missing index on frequently queried column
4. Why? → Index was dropped during migration
5. Why? → Migration script lacked index recreation step

Root Cause: Incomplete migration testing process
Solutions:
- Add index verification to migration checklist
- Implement automated index coverage tests
- Create pre-production performance benchmarks

Best Practices

Do

• Use data - Support answers with evidence and metrics
• Involve diverse perspectives - Different viewpoints reduce blind spots
• Focus on systems - Ask "what process failed?" not "who failed?"
• Document everything - Create audit trail for future reference
• Verify root cause - Test that fixing it would prevent recurrence

Avoid

• Stopping too early - Surface answers are usually symptoms
• Personal blame - "John made a mistake" is never the root cause
• Single path - Complex problems may have multiple root causes
• Assumptions - Always verify with data
• Skipping steps - Each "why" should logically follow the previous

Communication Tips

• Give people time to respond - embrace silence
• Ask one question at a time
• Resist the urge to clarify before they answer
• Focus on curiosity rather than interrogation
• Frame as collaborative problem-solving

Integration with Other Methods

The Five Whys works well alongside:

Resources

• Toyota Production System
• Taiichi Ohno's Workplace Management
• The Lean Startup - Eric Ries