Hey guys this is something i have been wondering about and id love to hear what you all think about the subject.
The theory is that whatever your habitual facial expressions are, after a while they begin to etch themselves on your face telling people what sort of human being you are. When your younger you have a clean slate but as you get older your face begins to reveal it more. In my experience this is true most of the time. Here ill let john cleese explain it better:
Sorry but you have to skip to 4:50 to get to the part i am talking about.