It shows us nothing more or less than the deepest, more desperate desire of our hearts. You, who have never known your family, see them standing around you. Ronald Weasley, who has always been overshadowed by his brothers, sees himself standing alone, the best of all of them. However, this mirror will give us neither knowledge or truth. Men have wasted away before it, entranced by what they have seen, or been driven mad, not knowing if what it shows is real or even possible.
When I die, I don’t want to go to heaven or hell. I want to stay on earth and haunt people. Turn the lights on in the kitchen when you thought you’ve turned them off. Hide under the bed and grab your leg when it dangles off while you’re sleeping. Sit in the backseat and show up in your rear-view mirror when you’re driving alone at night. Being a ghost sounds like a lot of fun!
The difference between how you look and how you see yourself is enough to kill most people. And maybe the reason vampires don’t die is because they can never see themselves in photographs or mirrors.