[who_would_fardels_bear]

In other news, there are only 21 reasons that account for 97% of traffic accidents, only 21 reasons that account for 97% of suicides, only 21 reasons that account for 97% of heart attacks, only 21 reasons that account for 97% of new diabetes cases, etc.

[CutePuppy]

See Pareto Principle (aka 80/20 Rule, Golden Rule, the Law of Vital Few, etc.), i.e. variations of 20% of "input" are responsible for 80% of "output".