Stupid is as Stupid Does

Forrest Gump's "Stupid is as stupid does" is a variant of an old adage: "Pretty is as pretty does” or, “Handsome is as handsome does." It basically means that true prettiness has to do with a person's behavior, not just a pretty face. 

Important because it all comes down to judging people by what they do, not by how they appear, or what you assume. A smart, talented person who does stupid things is still stupid.