The Pareto principle (also known as the 80'20 rule, the law of the vital few, and the principle of factor sparsity) states that, for many events, roughly 80% of the effects come from 20% of the causes.

Business-management consultant Joseph M. Juran suggested the principle and named it after Italian economist Vilfredo Pareto, who observed in 1906 that 80% of the land in Italy was owned by 20% of the population; he developed the principle by observing that 20% of the pea pods in his garden contained 80% of the peas.

It is a common rule of thumb in business; e.g., "80% of your sales come from 20% of your clients". Mathematically, where something is shared among a sufficiently large set of participants, there must be a number k between 50 and 100 such that "k% is taken by (100 ' k)% of the participants". The number k may vary from 50 (in the case of equal distribution, i.e. 100% of the population have equal shares) to nearly 100 (when a tiny number of participants account for almost all of the resource). There is nothing special about the number 80% mathematically, but many real systems have k somewhere around this region of intermediate imbalance in distribution.

The distribution shows up in several different aspects relevant to entrepreneurs and business managers. For example:

80% of your profits come from 20% of your customers
80% of your complaints come from 20% of your customers
80% of your profits come from 20% of the time you spend
80% of your sales come from 20% of your products
80% of your sales are made by 20% of your sales staff

Taken from : http://en.wikipedia.org/wiki/Pareto_principle

I am a believer of the above 80-20 concepts.

TEH