Refs need an education in basic psychology. Humans don't see what they aren't looking for, even if it is right in front of them. Instead, they do see what they ARE looking for, even if it doesn't happen.
That in a nutshell is what is wrong with reffing these days. Know the rules, enforce the rules, end of. They saw Hetho miss, because they are looking for him to break the rules. They don't see Walker pull scummy stuff in broad daylight because they aren't looking for him to do stuff. Refs need to be person-blind. Doesn't matter what your name is, the number on your shirt, the colour of your hair, or the badge on your jersey. If you break the rules, you get penalised/binned, etc. Get rid of the homework!