The Pareto principle, also known as the 80/20 rule, applies to most aspects of life. It is commonly explained as an asymmetric of outputs and inputs: 80% of your output comes from 20% of your inputs (the proportion may vary drastically). For instance, 80% of your revenue may come from 20% of your customers. This principle highlights the asymmetry of inputs and outputs, or the heterogeneous nature of inputs (not all inputs are created equal).
This teaches us that we can reduce our focus to only this high-leverage portion of inputs, actions, decisions, worries… that will make up most of the desired output.