Vilfredo Pareto

Vilfredo Pareto was a 19th century Italian economist, Vilfredo Pareto, who noticed that around 80% of the wealth of the country was held by around 20% of the population (and that this was recursive: of the 20%, 80% of their wealth was held by 20% of this privileged society, and so on).

Joseph Juran, a 20th century quality consultant (and guru), noticed that this also applied to defects, where around 80% of the problems would be in 20% of the defects, which meant that if you focused on that 20%, you could have a big effect with minimal effort. He called this the 'Pareto Principle'.

See also:

Toolbook chapter: Pareto Chart