Part of my Knowledge Base.
The Pareto principle (also known as the 80/20 rule, the law of the vital few, or the principle of factor sparsity) states that, for many events, roughly 80% of the effects come from 20% of the causesWikipedia.
The key insight is this: there is always a clever hack. The world is not fair. Effort is not distributed as it should be. And this isn’t because people are dumb, or not trying. This is the default state of the world. Allocating your effort efficiently is hard - if it wasn’t, then the Pareto Principle would not hold.