the Pareto principle
noun [ S ]
ECONOMICS, WORKPLACE, PRODUCTION ukus(also Pareto's law ); (informal the 80/20 rule)the idea that a small quantity of work or resources (= time, money, employees, etc.) can produce a large number of results:
The Pareto principle, when applied to time, states that 20% of your time determines 80% of your production.
The Pareto principle can be applied to quality improvement, as the majority of problems (80%) are produced by a few key causes (20%).