The 80/20 rule, also known as the Pareto principle, states that 80% of outcomes come from 20% of causes. It suggests focusing efforts on the 20% that provides 80% of the results. Specifically, identifying the key triggers or most important customers that generate most income and focusing resources on them, while reducing efforts on the remaining 80% that provides less value. Applying the principle across personal relationships, work, business, and more can help maximize productivity and results.