Sort of a complicated question, I'll try to ask. How was I born me and not another?

[EruptedCarcassBloat]

Again, if you're just talking about the potential combinations of your parents' genes, that's something we can work with, because that's a quantifiable number.  

But saying "You could have just as easily been the egg" doesn't make any sense still.  You're not now nor were you ever an egg or a sperm.

I think the question still remains though. Because there's so many possibilities of other people being born from the same mother, it seems improbable that you specifically were born from that mother, or anyone for that matter. That's not even to take into account the billions of years of evolution leading up to you being born. I just can't fathom how improbable my birth actually is.