5 Whys

The 5 Whys is a simple tool to drill down into the cause of a problem. The method was developed by Sakichi Toyoda. It is simple and easy to apply. The Toyota motor company recognized its significance and built the 5 whys method into their problem solving and continual improvement process.

Applying the 5 Whys

State the problem: My laptop computer will not start

1. Why will my laptop not start?  - The battery is dead
2. Why is the battery dead?  - The battery only retains it charge for a short period of time
3. Why does the battery only retain its charge for a short period? - The battery has lost its elasticity and no longer fully recharges
4. Why has the battery lost its elasticity and no longer fully charges?  - The battery has exceeded its maximum number of recharges
5. Why has the battery exceeded its maximum number of charges? - The battery is more than 3 years old and has been used every day

In general it is enough to ask why 5 times but this is just a guide.

Test the possible cause

Having completed the 5 whys and drilled down to what you think is a possible cause it is now important to explore and test that cause. State the possible cause and explore what it predicts. From the above example:

Problem: My laptop will not start

Possible Cause: the battery is old, it has been used every day for 3 years and it has exceeded its maximum number of recharges.

Prediction and Test: If this possible cause is true then what does it predict. For example a colleague has had his laptop for about the same time therefore the battery in his laptop should also be retaining its charge for a short period time. If the battery in the colleague’s laptop is still working fine then it is time to think again. If it is also failing then it is time to buy a new battery.