WHAT is it: The Pareto Principle 80/20 also known as the 80/20 Rule, illustrates that 80% of effects arise from 20% of the causes or that 20% of your actions/ activities will account for 80% of your results/outcomes. Mathematically, the 80/20 rule is roughly described by a power-law distribution for a particular set of parameters, and many natural phenomena have been shown to exhibit such a distribution. It is an adage of business management that "80% of sales come from 20% of clients".
HOW it works: If you look closely at the items on your "To Do" list, chances are only a few are tied to important issues. While it may be satisfying to cross off a large number of the smaller issues, the 80/20 rule suggests you focus on the few more important items that will generate the most significant results. The list might not grow much shorter, but you will be practicing effective prioritization.
Next, in assessing risks for an upcoming project, you'll find that not every risk carries equal significance. Select the risks that pose the highest potential for damage and focus your monitoring and risk planning activities on them. Don't ignore the others, just distribute your efforts proportionately.
BENEFIT/OUTCOME: Since 20% of your effort amounts to 80% of the effect of your work, you should consider which activities comprise the vital few you need to focus on. To maximize your efficiency, you must identify them and work on them first. Mind you, though, you should not neglect the other tasks. Pareto's principle is a useful construct when analyzing efforts and outcomes. It is valuable when applied to lists of tasks or goals. It can provide a useful framework for addressing many problems.