Source
Pareto principle (the 80/20 rule)
The observation that, for many outcomes, roughly 80% of effects come from 20% of causes. It is named after the Italian economist Vilfredo Pareto, who noted that about 80% of the land in Italy was owned by 20% of the people; Joseph Juran generalised the idea and gave it its name.
References
Quotes (1)
“For many outcomes, roughly 80% of consequences come from 20% of causes.”
— Joseph M. Juran (after Vilfredo Pareto), Pareto principle, as summarised by Wikipedia (paraphrase, not a direct quote)