From the viewpoint of an atheist, when you die, you cease to exist. Your brain has grown old, and can no longer sustain the trillions of electrical signals that constituted who you once were. Similarly, before you were born, this same series of electrical connections did not exist yet, and not much different from a state of post-death, you were completely unaware of anything at all. You did not exist.
I don't precisely know why, but this seems spooky to me. There was a point when all of us had been in this state of complete blackness. Non-existence. But, now we're here. You could say it was nature that brought us into existence. A combination of our parents' DNA mixed in with some environmental circumstances to format the neural connections that make you, you. In this case, it seems up to random forces that determine whether an individual will exist or not.
But who is to say that this materialization into existence cannot happen multiple times? Perhaps death is not an ending, but rather a time frame of non-existence, until probabilistic forces are able to construct a similar set of neural pathways. Maybe this question is out of the scope of this site, but I am curious to see a philosophical approach to the concept.