The Pareto Principle, also known as the 80/20 rule, is an observation that states that roughly 80% of the effects come from 20% of the causes. This principle was named after Vilfredo Pareto, an Italian economist who observed in the early 1900s that 80% of the land in Italy was owned by 20% of the population.

The Pareto Principle has since been applied to many different areas, including business, economics, and personal productivity. For example, it is often observed that 80% of a company's revenue comes from 20% of its customers, or that 80% of a person's success in their job comes from 20% of their efforts.

The Pareto Principle is not a hard and fast rule, but rather a generalization based on observations. However, it can be a useful tool for identifying areas where a small amount of effort can have a large impact, or for focusing on the most important aspects of a problem or situation.