80/20 Principle is terrific. An Italian Vilfredo Pareto who lived from 1823 to 1923 was the first one to demonstrate the 80/20 rule. According to him the minority of events cause major results. He stated the principle of Least Efforts. His rules are known as Pareto Law or Pareto Principle and by many other names.
He was analyzing the distribution patterns of wealth and income in England. An important conclusion of his discovery was that, the majority of income and wealth was with minority of people. Analyzing further he came to know that wealth distribution was imbalanced not only in England but in whole of the world. Digging out further he found that, this imbalance existed everywhere in the world. Means not only in economy but in every sphere of life.
Six Sigma also uses this theory. This rule is also used in Six Sigma to improve quality and decrease number of defect by controlling minority of parameters. This kind of analysis is also called Pareto Analysis.