You probably have heard about the Pareto Principle.

The Pareto principle states that for many outcomes, roughly 80% of consequences come from 20% of causes (the "vital few").^[1] Other names for this principle are the 80/20 rule, the law of the vital few, or the principle of factor sparsity.^[2][3]

Management consultant Joseph M. Juran developed the concept in the context of quality control, and improvement, naming it after Italian economist Vilfredo Pareto, who noted the 80/20 connection while at the University of Lausanne in 1896.^[4] In his first work, Cours d'économie politique, Pareto showed that approximately 80% of the land in Italy was owned by 20% of the population. The Pareto principle is only tangentially related to Pareto efficiency.

Mathematically, the 80/20 rule is roughly described by a power law distribution (also known as a Pareto distribution) for a particular set of parameters, and many natural phenomena have been shown to exhibit such a distribution.^[5] It is an adage of business management that "80% of sales come from 20% of clients".^[6]

Source: https://en.wikipedia.org/wiki/Pareto_principle