The fact that you exist and are aware enough to believe anything at all is so stupendously unlikely that the only possible explanation is that you're living in one of the only universes where it's possible for you to live, and have consciousness; that's the only one you're conscious of, because it's the only one you can be conscious of.

Ultimately though, from the time you're born, the number of universes you can possibly exist in will get fewer as more and more branches lead to death. You'll only be aware of the ones you still survive in, of course, but those will probably include fewer and fewer people.

Eventually, you'll be the last living person. Lonely, miserable and immortal.