Basically Pareto principle raises a general rule by which 80% of the effects come from 20% of causes.
Was named back in the 40s by Joseph M Juran after the Italian economist Vilfredo Pareto (1848-1923). Pareto confirmed the application of this rule in italian wealth distribution as well as in other curious phenomena such as the 20% of the peapods in his garden contained 80% of the peas.
Although the 80/20 values are a good reference, this principle has an empirical basis, we are not talking about an exact formula. In summary what it means is that within any system, only a few main variables affect the outcomes and most other factors will return little or no impact.
Within the scope of product design it is interesting to consider this principle either in the definition work, interface design or user testing.
A simple rule which can help us understand certain phenomena that occur in design processes, and put the focus on the aspects that bring more value to our products.