The 80/20 Ratio (Pareto Principle)

This principle is useful in deciding where to focus effort and resources. In essence, it states that 80% of output is produced by 20% of input.
Common examples of this include:
80% of revenue comes from 20% of clients
80% of problems comes from 20% of causes
80% of results comes from 20% of efforts
80% of profit comes from 20% of products.
This principle can be useful for planning or decision making, either in business or in your personal life to identify where to concentrate efforts to make changes.