You won't know wtf you are talking about.
When you look in the mirror, your right eye can see the left eye and vice versa. How hard is that to understand?
For example, holy fuck, it's hard for me to understand how stupid some people can be.
This isn't something for you to get all cuzzy about dude, so calm down. In this case, the riddle didn't ask this "what is use to reveal the brother who never see "themselves" and "each other?" In this case, it would be a mirror. But, the answer wasn't asked like that, and the answer here isn't a "mirror" either. The answer here is your "eyes". Without your eyes, the mirror is useless. Again, the riddle did not ask for an object that reveals the brothers, if it did it would be a mirror. Read the riddle and take it as it is, not defer things out of context to what it isn't and should be.
Six one from the bottom:http://www.blackdog4kids.com/games/word/riddles.html