Why is this the answer?

The answer is mirror because this clever riddle uses fun, tricky words to describe an object you see every day that loves to show you a perfect picture of yourself. Let us look at the first clue: “Look into my face and I'm everybody.” Think about the smooth, shiny surface of a mirror. That shiny part is what the riddle calls its "face." When you stand in front of it, what do you see? You see your own reflection looking right back at you! The mirror does not have a picture of its own that stays there forever. It is ready to show the reflection of your best friend, your teacher, your mom or dad, or anyone else who steps up to look at it. Because the mirror can show a clear picture of *every single person* who looks, the riddle says it is "everybody." It is like the mirror has a thousand different faces ready to show the world, all because of a special trick that science and light help the mirror do. The mirror is a perfect copycat for anyone who stands before it. Now, let us think about the second, trickier clue: “Scratch my back and I'm nobody.” A mirror is not shiny and special all the way through. The secret to its trick is on its back. If you flipped a regular mirror over, you would see that the glass is covered with a very thin, special coat of shiny metal or paint. This thin, hidden layer is what does all the work to make the glass reflective. The riddle calls this the "back." If you were able to "scratch" or rub off that special paint on the back of the glass, the shiny surface would not work anymore. The reflection would disappear! Instead of seeing a person's picture, you would just see a plain, unexciting piece of glass. When the mirror loses its power to show a person's picture because its back is scratched, it loses its identity and becomes "nobody." The riddle shows us that a mirror is only important and only "somebody" because of the hidden magic on its back.