Comment by pixl97

https://en.wikipedia.org/wiki/Sorites_paradox

This is the problem of describing if a gradient has something. Quite often the 'N tests' we make up end up excluding entire classes of humans (You're blind, oops!) by poor premise in our classifications.

People love black and white/binary classification systems, the problem with reality is it rarely gives a damn about giving us simple systems to classify that way.