If you wanna go even deeper into the formation of an embryo stage, you know, millions of sperms are released each time you ejaculate. Let take this number as 400 million. Average human male ejaculates 7500 times in his life time.

400 * 7500 = 3000000(3 billion)


Add this variables to your thinking and equation odds become even less likely. 

Just because odds are less likely doesn't mean it can never happen. Because the answer is you.