How Harry survived Voldemort's attack

'I have many questions for you, Harry Potter. How is it that a baby with no extraordinary magical talent managed to defeat the greatest wizard of all time? How did you escape with nothing but a scar, while Lord Voldemort's powers were destroyed? Twice - in your past, in my future - we have met. And twice I failed to kill you. How did you survive?
'No one knows why you lost your powers when you attacked me. I don't know myself. But I know why you couldn't kill me. Because my mother died to save me. My common Muggle-born mother. She stopped you killing me. And I've seen the real you, I saw you last year. you're a wreck. You're barely alive. That's where all your power got you. You're in hiding. You're ugly, you're foul!'
'So. Your mother died to save you. Yes, that's a powerful counter-charm. I can see now - there is nothing special about you, after all. I wondered, you see. Because there are strange likenesses between us, Harry Potter. Even you must have noticed. Both half-bloods, orphans, raised by Muggles. Probably the only two Parselmouths to come to Hogwarts since the great Slytherin himself. We even look something alike... But after all, it was merely a lucky chance that saved you from me. That's all I wanted to know.'

THE HEIR OF SLYTHERINE - Pg 330