"Ask 'why' five times about every matter." -- ROOT cause analysis

Taiichi Ohno,(Former Executive Vice President of Toyota Motor Corporation )

used the example of a welding robot stopping in the middle of its the operation to demonstrate the usefulness of his method, finally arriving at the root cause of the problem through persistent inquiry:

1. "Why did the robot stop?" The circuit has overloaded, causing a fuse to blow.
2. "Why is the circuit overloaded?" There was insufficient lubrication on the bearings, so they locked up.
3. "Why was there insufficient lubrication on the bearings?" The oil pump on the robot is not circulating sufficient oil.
4. "Why is the pump not circulating sufficient oil?" The pump intake is clogged with metal shavings.
5. "Why is the intake clogged with metal shavings?" Because there is no filter on the pump.

Courtesy :
http://www.toyota-global.com/company/toyota_traditions/quality/mar_apr_2006.html

Asking why 5 times: “the 5 Whys”, is a simple but powerful tool to use with any problem-solving activity. It’s a technique to help you get past the symptoms of a problem and to find its root causes. Simply ask the question “why” up to five times. Of course, there’s no magic in this number of questions.
It may take six or it may take three. The important thing is that you use this most powerful of words to peel away the layers that envelope any problem. It’s so simple, even a child could use it – and they do! This may look familiar to many of you:
“Why do I have to go to bed?” – “Because you need your sleep.”
“Why do I need to sleep?” – “Because it’s good for you.”
“Why is it good for me?” – “Because your body needs regular rest.”
“Why does my body need rest?” – “Because resting helps you re-charge your battery.”
“Why do I need to re-charge it?” – “Because otherwise you’d have no energy to enjoy tomorrow.”

The main problem of these decisions is not seeing the root cause. The root cause analysis is one of the most fundamental concepts to improve any process or solve any issue