5 Why
Explore the cause-and-effect relationships underlying a particular problem - determine the root cause of a defect or problem by repeating the question “Why?” five times
- Snippet from Wikipedia: Five whys
Five whys (or 5 whys) is an iterative interrogative technique used to explore the cause-and-effect relationships underlying a particular problem. The primary goal of the technique is to determine the root cause of a defect or problem by repeating the question "why?" five times, each time directing the current "why" to the answer of the previous "why". The method asserts that the answer to the fifth "why" asked in this manner should reveal the root cause of the problem.
The technique was described by Taiichi Ohno at Toyota Motor Corporation. Others at Toyota and elsewhere have criticized the five whys technique for being too basic and having an arbitrarily shallow depth as a root cause analysis tool (see § Criticism).