Vilfredo Pareto, Italian economist define Pareto principle. He found that 80% of assets in Italy is held by 20% of the population. Pareto principle reads 80% effect is caused by only 20% of the causes. If we want to eliminate 80% of the losses, focus activities only predefined problems in the range of 20%.
Pareto principle gave rise to Pareto analysis, which is used for troubleshooting through the most important causes see Pareto analysis.