When I was a boy, my grandmother used to read me nursery rhymes to entertain me and teach me about the world. One has resonated with me for years:

"For want of a nail the shoe was lost
For want of a nail the horse was lost
For want of a horse the warrior was lost
For want of a warrior the battle was lost
For want of a battle the kingdom was lost
All for the want of a nail."

This little poem displays the heart of the five-why problem-solving method that’s used mainly in the automobile industry, especially the Japanese auto industry. Basically, five-why analysis is a fundamental approach to thinking, based on the logical linkage of elements into a cause-and-effect analysis. Look at a problem and ask yourself, “Why did this happen?” Then with each specific answer, repeat the question about five times and you will typically end up with a rather solid root cause. In the poem above, the problem was that the kingdom was lost. The series of why questions leads you through the loss of the battle due to not enough soldiers, and ultimately due to not enough nails in the hands of the blacksmiths.

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