80/20 principle misunderstanding

I often read online articles written by people who misunderstand the 80/20 principle. Here are the most common misconceptions about the 80/20 rule:
Two different things
Basically the 80/20 rule says :
80% of the output comes from 20% of the input.
80 and 20 are percentages of different things. Input and output aren’t the same things, it’s two [...]