They say there are up to 7 people (although some sources on the Internet say 6) in the world who look exactly like you. If this is actually true, with a global population of over seven billion, you can say that roughly 1 in every 1 billion people look identical to you. So in your lifetime, your chances of actually running into your lookalike are slim to none.
Despite physical differences, humans are 99.9% identical in their genetic makeup. It is that tiny .1% that gives us all a unique appearance. This is definitely a good thing. Could you imagine a world where everyone looked the same?