Richard Koch. The 80/20 principle: the secret of achieving more with less. New York, The Doubleday, 2008.

"The pattern of predictable imbalance underlying the 80/20 Principle was first discovered a hundred years ago by Italian economist Vilfredo Pareto while studying income and wealth patterns. But the pattern of "predictable imbalance," as he termed it, crops up throughout life. In The 80/20 Principle, Koch opens our eyes to the way the principle works through a wide range of examples in business, commerce, and virtually every aspect of our lives. For example, 20 percent of products account for 80 percent of sales and profits; similarly, 20 percent of customers account for 80 percent of revenues.".