That person/persons who remind you to look at your situation in a different light by comparing it with the situation of themselves or others.They usually spring into action when you are feeling sorry for yourself or you think things are going badly for you.
Guy 1- "Holy crap it's hot out here! It must be at least 90!"
Guy 2 - "Time to call the Perspective Police. It could be worse man, at least you're not stuck in the deserts of Iraq like Joe."