The document discusses the Pareto principle, also known as the 80/20 rule, which states that roughly 80% of outcomes or results come from 20% of causes, efforts, or inputs. The principle is described as applying to many business, economic, and quality control situations. Some examples given include that 80% of sales come from 20% of customers, 80% of profits come from 20% of products, and 80% of work gets done in 20% of the time. The principle is presented as a useful heuristic for focusing efforts on the most important causes or inputs.