There are, of course, an incredible amount of theories on how Harry Potter survived. Problem is that the most important one, the one that is canon, is the one I don't get: how Harry's blood inside Voldemort saves him?
Because all that I have read so far, leaves me with questions. I understand why Voldemort wanted Harry's blood, but why does it save Harry? Why is that necessary to keep the sacrifice alive, while it's still inside Harry? And if Harry lost it at 17 (I have seen some different ideas on this as well), why does Voldemort still have it at 69 (give or take a few)?
To clafiry, the parts I'm talking about:
"For a fleeting instant, Harry thought he saw a gleam of something like triumph in Dumbledore's eyes"
(GoF, right after Harry tells Dumbledore that his blood now goes through Voldemort.)
"He took your blood believing it would strengthen him. He took into his body a tiny part of the enchantment your mother laid upon you when she died for you. His body keeps her sacrifice alive, and while that enchantment survives, so do you"
(Albus Dumbledore in DH)
I just don't get why the blood transfusion thing suddenly gave Harry the chance to survive the whole thing, and it's never really been satisfyingly answered, not to my knowledge at least, as every answer I've read raises more questions.