The 80/20 rule, also known as the Pareto principle, is the idea that roughly 80% of outcomes result from 20% of causes. It describes a common imbalance observed in many real-world systems, where a small number of factors account for a large portion of results. Though not a strict mathematical law, this rule is widely used in business, economics, quality control, and data analysis to identify areas of high impact.
The principle was first observed by Italian economist Vilfredo Pareto in the late 1800s, when he noticed that about 80% of the land in Italy was owned by 20% of the population. Over time, this pattern was found in a variety of contexts, such as income distribution, productivity, and even software errors. The rule has since been generalized to reflect many skewed distributions in statistics, especially those related to power laws and long-tail phenomena.
For example, in business, a company may find that 80% of its sales come from just 20% of its customers. Recognizing this pattern can help the company focus its marketing efforts and customer support where they matter most. While the exact ratio may differ—such as 70/30 or 90/10—the underlying idea remains the same: a small number of inputs often drive a large share of results.
« Back to Glossary Index