5 Whys
The 5 Whys is a root-cause analysis technique that asks why a problem happened about five times in succession to trace it back to its underlying cause.
The 5 Whys became widely known as a problem-solving method in the production system of Japan's Toyota. Starting from an observed problem, it asks why the problem occurred, then asks why again about each answer, moving past surface symptoms toward the underlying cause. The number five is a rule of thumb rather than a fixed requirement.
Although it began in manufacturing, the technique is also used in software development and IT operations, for example in reviews held after an outage to trace its cause.
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