The 5 Whys Investigation Technique

5 Whys

Ask "Why?" repeatedly (usually 5 times) until you reach the underlying cause.

State the problem.
Ask "Why did this happen?"
For each answer, ask "Why?" again.
Continue until you reach a process, system, or management issue that can be fixed.

Example:

Tips for Effective 5 Whys

• Why did the machine stop? → Fuse blew.
  
• Why did the fuse blow? → Motor overloaded.
  
• Why was the motor overloaded? → Bearing wasn't lubricated.
  
• Why wasn't it lubricated? → Maintenance was missed.
  
• Why was maintenance missed? → No maintenance schedule existed.

A good 5 Whys analysis doesn't end with "someone made a mistake."

It usually ends with a process, training, system, or control weakness that can be improved.

• Focus on facts, not assumptions.
• Avoid blaming people; look for process and system causes.
• Verify each answer with evidence.
• Stop when fixing the identified cause would prevent the problem from recurring.