The 80-20 rule is also popularly known as the Pareto principle. It states that 80% of the outcomes come from just 20% of the causes in life. So, 80% of the outcome comes from 20% of the time spent, and the remaining 20% of the outcome comes from 80% of the time spent. In the book “4-Hour Workweek”, the author tries to optimize the 80/20 rule such that one can make more money by consuming less time. The idea is to focus on the 20% of the time that gives 80% of the outcome and leave the remaining 20% of the outcome that consumes most of your time to do some other task that adds more value.