This is one of the things I first look for, and notice, about people when I meet them.
I'm certainly no expert, but from what I've read and gathered, it has a lot to do with a person hiding something and it so psychologically affects them that it begins to portray itself on their face, typically through one side in particular - as if they are living double lives, and are two different people.
My belief is that this is especially prevalent in these cabal-involved individuals, and if you really look for it, a lot of the times you will find it.