Richard Koch

Twenty percent of those who marry comprise 80 percent of the divorce statistics

He happened to be looking at patterns of wealth and income in nineteenth-century England. He found that most income and wealth went to a minority of the people in his samples. Perhaps there was nothing very surprising in this. But he also discovered two other facts that he thought highly significant. One was that there was a consistent mathematical relationship between the proportion of people (as a percentage of the total relevant population) and the amount of income or wealth that this group enjoyed.4 To simplify, if 20 percent of the population enjoyed 80 percent of the wealth,5 then you could reliably predict that 10 percent would have, say, 65 percent of the wealth, and 5 percent would have 50 percent. The key point is not the percentages, but the fact that the distribution of wealth across the population was predictably unbalanced.

Zipf’s principle said that resources (people, goods, time, skills, or anything else that is productive) tended to arrange themselves so as to minimize work, so that approximately 20–30 percent of any resource accounted for 70–80 percent of the activity related to that resource.7