I've just had a quick look for the origin of the 80/20 rule - an expression used ad-nausia in standards when asserting what is the most common use-case.

This is often attributed as The Pareto Principle named after Vilfredo Pareto, an Italian economist who studied the distribution of wealth in a variety of countries. His law of the vital few and the principle of factor sparsity states that for many phenomena 80% of consequences stem from 20% of the causes.

However, several other sources describe how Joseph Juran, the quality management guru, formalised a universal principle he called the "vital few and trivial many" and first coined the term "80/20".

Looking on Google, the split between Pareto/Juran is roughly 80/20 :^)

updated to fix broken Pareto link