What is the principle and how can it help?

The Pareto principle (also known as the 80/20 rule) states that for many phenomena 80% of consequences stem from 20% of the causes. The idea has rule-of-thumb application in many places, but it's also commonly misused, for example, it is a misuse to state that a solution to a problem 'fits the 80-20 rule' just because it fits 80% of the cases; it must be implied that this solution requires only 20% of the resources needed to solve all cases.

The principle was in fact suggested by management thinker Joseph M. Juran and it was named after the Italian economist Vilfredo Pareto, who observed that 80% of property in Italy was owned by 20% of the Italian population. The assumption is that most of the results in any situation are determined by a small number of causes.

So '20% of clients may be responsible for 80% of sales volume'.  This can be evaluated and is likely to be roughly right, and can be helpful in future decision making. The Pareto Principle also applies to a variety of more mundane matters: one might guess approximately that we wear our 20% most favoured clothes about 80% of the time, perhaps we spend 80% of the time with 20% of our acquaintances and so on.

The Pareto principle is unrelated to Pareto efficiency, which really was introduced by Vilfredo Pareto. Vilfredo Pareto (born July 15, 1848 in France - died August 19, 1923 in Lausanne, Switzerland) made several important contributions to economics, sociology and moral philosophy, especially in the study of income distribution and in the analysis of individuals' choices. He introduced the concept of Pareto efficiency and helped develop the field of microeconomics with ideas such as indifference curves. In 1906, he made the well-known observation that 20% of the population owned 80% of the property in Italy, later generalised (by Joseph M. Juran and others) into the so-called Pareto principle (for many phenomena 80% of consequences stem from 20% of the causes), and generalised further to the concept of a Pareto distribution.

The Pareto Principle or 80/20 rule can and should be used by every smart but lazy person in their daily life. The value of the Pareto Principle for a project manager is that it reminds you to focus on the 20 percent that matters.

Woody Allen once said '80% of success is showing up', I'm not so sure about that, I have seen projects where there was a physical project manager around but you would never have believed that looking at the project progress, or lack of progress.

No, better I believe to appreciate that of the things you do during your day, only 20 percent really matter.

Those 20 percent produce 80 percent of your results.

So, you should identify and focus on those things during your working day.

Do this well and you will enjoy the world of 'Productive Laziness'.