80/20 rule

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, 80% of the effects come from 20% of the causes. It's named for an Italian economist, Vilfredo Pareto, who noticed that in his country 80% of the wealth was owned by 20% of the population.

Pareto's Principle, the 80/20 Rule, should serve as a daily reminder to focus 80 percent of your time and energy on the 20 percent of you work that is really important. Don't just "work smart", work smart on the right things.