Pareto principle
Etymology
An eponym: Italian economist Vilfredo Pareto noted around 1896 that about eighty percent of Italy’s land was owned by twenty percent of the people. The management thinker Joseph Juran later generalized it and named it the “Pareto principle,” also calling it the 80/20 rule.
noun phrase · /puh-RAY-toh PRIN-suh-puhl/
The observation that roughly eighty percent of effects come from twenty percent of causes.
What it names
A recurring lopsidedness in the world — that a small share of inputs drives most of the output — turning a vague sense of imbalance into a usable rule of thumb.
Example
Applying the Pareto principle, she found that a fifth of her clients generated four-fifths of the revenue and focused there.
Related idea
Not to be confused with Pareto efficiency, a separate idea from the same economist about allocations that cannot be improved for one party without harming another; the principle is about skewed distributions, the efficiency about optimal trade-offs.