I think this person is referring to the 80/20 rule. Here are a few examples:

20% of a plant contains 80% of the fruit

80% of a company’s profits come from 20% of customers

20% of players result in 80% of points scored

I've heard this stated as you can complete 80% of a project with 20% of the effort, and the last 20% of completeness will require 80% of the effort.