What is the Pareto Principal?

http://en.wikipedia.org/wiki/Pareto_principle

The pareto principle (AKA 80:20 Rule)

The so-called Pareto principle (also known as the 80-20 rule, the law of the vital few and the principle of factor sparsity) states that for many phenomena 80% of consequences stem from 20% of the causes. The idea has rule-of-thumb application in many places, but it is commonly misused.

The principle was suggested by management thinker Joseph M. Juran. It was named after the Italian economist Vilfredo Pareto, who observed that 80% of property in Italy was owned by 20% of the Italian population. (Since J. M. Juran adopted the idea, it might better be called "Juran's assumption".) The assumption is that most of the results in any situation are determined by a small number of causes. This idea is often applied to data such as sales figures: "20% of clien