Roughly 80% of the outputs come from 20% of the inputs. This applies to many events observed in the world of economy, biology, computing, sport and many other areas.

Examples:

• Sometimes when my kitchen becomes a mess and I don’t have 20 min for a comprehensive clean-up I am doing a 2 min cleanup. It is incredible how much one can achieve in two minutes and later on the task of finishing the cleanup doesn’t seem that big.
• More

Other names: Pareto principle (see Pareto Principle on Wikipedia)