Law of Vital few and Trivial many

Also known as “The Pareto Principle” or “80/20” rule. In a large system, a high percentage of effects come from a low percentage of causes.

This rule declares that the majority(70 - 90 %) of effects in a large system are caused by a minority (10-30%) of variables in that system. Surprisingly this rule works in a wide range of systems that can comprise of engineering, economics, design, project management etc.

Examples

80% of the errors are caused by 20% of the code
80% of the revenue comes from 20% of the customers
80% of time is spent using 20% of a product’s features
80% of the wealth is owned by 20% of the population
80% of class reputation is due to 20% of students

This is especially a good rule to keep in mind while designing. Designers could use this rule to improve and work on the 20% features the users actually use 80% of the time. Designers should test and concentrate on that 20% of features. A good use of this rule also includes, hiding away the 80% less-used parts of the system, in many cases eliminate them from the system.

Real World Examples

Country Selection Dropdown

In this use case we can observe the few countries selected and placed above in its own separate section thus applying the 80/20 rule. To eliminate this altogether, we can just have a default selection of the relative country.