80/20 rule or rule of vital few
says that roughly 80% of consequences come from 20% of causes
in Economics - “80% of sales come from 20% of clients” Pareto noticed that approximately 80% of Italy’s land was owned by 20% of the population
In Computers optimization - Microsoft noted that by fixing the top 20% of the most-reported bugs, 80% of the related errors and crashes in a given system would be eliminated. - 80% of a piece of software can be written in 20% of the total allocated time - 20% of the code has 80% of errors
see also sturgeons law