Are you your brain? Is your conscious self born from your grey-matter? Let's be radical and assume it is. For the sake of a little thought experiment.
A viable brain is born. It's structure determined partly by inheritance and partly by chance. Then another. And another. A train of brains. Conscious folk being produced one by one. You are to be number 57. But wait. Something happens. The brain that was to be number 57 is squished before it can develop. Kicked off the line. Ejected. Does that mean you never exist? Or are you now the one that would have been number 58?