From Funders and Founders, an infographic that backs up the old 80/20 rule. From Wikipedia, the definition of the Pareto Principle: “The Pareto principle (also known as the 80–20 rule, the law of the vital few, and the principle of factor sparsity) states that, for many events, roughly 80% of the effects come from 20% of the causes”
I have used this rule all my business life. It works. It should define how you run your business.