The 80/20 rule asserts that approximately 80% of effects or consequences come from 20% of causes or inputs. This principle, also known as Pareto's principle, is observed across many systems involving large numbers of variables. In design, the 80/20 rule suggests focusing resources like design, testing, and innovation efforts on the critical 20% of features, components, or people that drive 80% of key outcomes like usage, revenue, errors, or progress. Applying the principle can help realize greater efficiencies.