The Pareto principle is the 80-20 rule. Meaning if there are 4 great filters each with an effectiveness of 0.9,0.9,0.99, and 0.9, it will be the 0.99 filter that requires ten times the attention / luck and will get the name 'Great', even if there are many other hurdles adding to the end result.

This is a troubleshooting problem where we are still on the first stage of the diagnosis: Identifying the largest contributor to the problem, identifying the low hanging fruit. The whole filter that prevents life on every planet is going to the a combination of many stacked smaller filters, but we want to find the most relevant filter, either the 0.999 filter or the locally relevant filter. This discussion is all part of that diagnostic process to find the most relevant single cause.