The Pareto principle states that for many outcomes, roughly 80% of consequences come from 20% of causes (the “vital few”). Other names for this principle are the 80/20 rule, the law of the vital few, or the principle of factor sparsity. - Wiki
I only recently came across this principle a few months back while doing Ali Abdaal's wonderful Skillshare course. It has made me reconsider all of the decision making that goes onto my projects and actions in life.
it might be the case that 80 percent of a business’s profits come from just 20 percent of its clients, 80 percent of a nation’s wealth is held by its richest 20 percent of citizens, or 80 percent of computer software crashes come from just 20 percent of the identified bugs. - Cal Newport (Deep Work)
From the lens of time management and prioritizing, this law is especially useful when one considers that 80% of your output is basically a result of 20% of your actions. Thus also effectively stating that anything you put beyond the 20% is going to give you radically reduced diminishing returns.
The catch is to define the 20% effectively, spend a reasonable amount of time in defining which are the tasks that need your attention the most out of all the things that you do in a day.
Newport in his book also goes as far as to encourage that one should eliminate the 80% tasks that give you reduced returns as the brain doesn't distinguish between a high priority task and a low one, and that the overhead on your mental energy is the same as long as you don't stop entirely doing the tasks that don't align to your desired outcomes.
all activities, regardless of their importance, consume your same limited store of time and attention. If you service low-impact activities, therefore, you’re taking away time you could be spending on higher-impact activities. It’s a zero-sum game. And because your time returns substantially more rewards when invested in high-impact activities than when invested in low-impact activities, the more of it you shift to the latter, the lower your overall benefit.- Cal Newport