The Pareto Principle simply states that 80% of the results come from 20% of the effort.
Thus, the 80/20 rule.
For example:
80% of your income comes from 20% of your clients
80% of your complaints come from 20% of your customers
80% of your engagement comes from 20% of your content
80% of your creativity comes from 20% of your inspiration
80% of your skill set comes from 20% of the material
Not part of the Pareto Principle but works with the 80/20 rule:
80% of sales require 5 follow-up calls after the meeting. And 20% of sales will take a year to buy!