Something that tends to get referenced more and more is the 80/20 rule or the Pareto Principle What it states is that approximately 80% of the effects generated by any large system are caused by 20% of the variables in that system. Its origins stem back to Vilfredo Pareto, an economist who noticed 80% of Italy’s land was owned by 20% of the population.

Some more examples of the rule: 

80% of a towns traffic is on 20% of it’s roads
80% of innovation comes from 20% of the people
80% of a products usage involves 20% of it’s features.
80% of a company’s revenue comes from 20% of it’s products. 
80% of progress comes from 20% of the effort

The crux of the principal lies in knowing that, within any system, only a few main variables affect the outcomes, and most other factors will return little or no impact. So if we have a set amount of time and energy let’s figure out what matters the most and then invest our time and effort into the areas what will deliver the greatest impact. 

Design smarter :)