5 Whys
A root cause analysis technique that repeatedly asks 'why' to move from a problem to possible underlying causes. Five questions is a guideline, and the answers need evidence.
THE IDEA
The 5 Whys Technique
The 5 Whys uses repeated 'why' questions to investigate a problem. Each answer suggests a cause to check and a starting point for the next question. The aim is to find causes that can be addressed; reaching five questions does not establish that the analysis is complete.
How It Works
- Start with a clear description of the problem.
- Ask 'why' the problem occurs.
- For each answer, ask 'why' again.
- Continue while further questions reveal causes worth investigating (often after 4–6 iterations).
- Check the proposed cause and address it; then monitor whether the problem recurs.
Example from the Text
- Why do I want to move? Because I want to explore a new place.
- Why do I want to explore a new place? Because I feel I might be limited where I am now.
- Why do you think you will be trapped in your same home? I can’t explore where I am. I want to try new things. New experiences shape life, right?
- Why can’t you go on day trips and explore from your new home? That’s a good question… Maybe I could explore the world around me without having to move.
- Why don’t you explore new places now? There is no reason I don’t. So, I guess I will! Let me try that before I commit to a big move.
Key Points
- The number 5 is a guideline; some problems may need fewer or more iterations.
- Answers should be based on facts, not assumptions.
- The technique works well for simple to moderately complex problems.
- It is often used in Lean, Six Sigma, and Toyota Production System.
Limitations
- May oversimplify problems with multiple interdependencies.
- Results depend on the knowledge and bias of the person asking the questions.
When to use it
Investigating a manufacturing defect on an assembly line.
Understanding the reason for a recurring customer complaint.
Uncovering why a personal habit (e.g., procrastination) persists.
Analyzing the cause of a missed deadline in a team project.
FROM THEORY TO EVERYDAY LIFE
In practice
Personal Decision: To Move or Not
- Why do I want to move? I want to explore a new place.
- Why do I want to explore a new place? I feel limited where I am now.
- Why do I feel trapped in the same home? I want new experiences and have assumed I cannot find them here.
- Why not take day trips from my current home? That may offer some of the exploration I want.
- Why am I not exploring nearby places now? I have not tried. I can test that option before committing to a move.
Business Example: Machine Stops
- Why did the machine stop? A fuse blew.
- Why did the fuse blow? The machine was overloaded.
- Why was it overloaded? The bearing was not lubricated.
- Why was it not lubricated? The pump was not circulating oil.
- Why was the pump not circulating oil? The pump shaft was broken.
The broken shaft is a cause to investigate and repair. Checking why it broke may reveal a further maintenance or design issue.
A MOMENT TO REFLECT
Put it to work.
Think of a recent problem you faced. Apply the 5 Whys to see if you can uncover a deeper cause.
How might the 5 Whys fail if the person answering lacks knowledge or avoids the real issue?
In the moving example, what would have happened if the questioning stopped at 'Because I want to explore a new place'?
Often confused with
CONTINUE THE CONVERSATION
Source texts
- Thinking in Systems and Mental Models Think Like a Super Thinker (Dawson, Marcus P)