80-20 Rule

So there's this idea that's going around now days, that 80% of the sum total of something is the result of 20% of the sources. This is often exemplified from such examples as 80% of the worlds income belonging to 20% of people. 80% of your uni grades comes from 20% of your study (I may or may not have taken advantage of this while getting my 80% average at uni!)

Far from being an exact formula, it's more of a rule of thumb used as an alternate way of thinking about things.

Something that is interesting to think about is that it can more or less be applied to skills as well. 80% of a skill comes from 20% of the practice & learning. And the final 80-20 heuristic I'll be touting is this: 80% of the perceived skill comes from 20% of the techniques. So you can seem like you are 80% good at something when you really only know/can do 20% of it.