The 80:20 Principle is a mental representation from Vilifredo Pareto, an Italian economist. Up to 80% of what you want to do can be accomplished in 20% of the expected effort. Examples: 80% of profits come from 20% of products; 20% of baggage screeners account for 80% of mistakes according to the New York Times. (Gardner, Howard. Changing Minds. MA: Harvard Business School Press, 2006, pp 7-8)

A minority of causes, input, or efforts usually lead to a majority of results, outputs or rewards. (Koch, Richard. The 80:20 Principle. NY: Currency Doubleday, 1999, pp 3-4)