Update: This post has also been superseded - new comments belong in the latest thread.
The second thread has now also exceeded 500 comments, so after 42 chapters of MoR it's time for a new thread.
From the first thread:
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I'm still trying to figure out what happened at Godric's Hollow.
Voldemort went in there with the intention to kill Harry (evidence: the prophecy, his seeming willingness to let Lily escape). Lily asked him to spare Harry's life in exchange for her own. It would seem that Voldemort accepted this offer in some way: he verbally agreed to the bargain, he killed Lily despite a previous intention to spare her, and Harry ended up surviving the encounter. But why would Voldemort do that when he could as easily have killed both, when he wanted Harry dead for prophecy-related reasons, and when he wanted Lily alive for Snape's sake?
Theories:
Voldy had always planned to save Harry's life for his own purposes - maybe he interpreted the prophecy as meaning this would be the boy into whom he could upload his personality. He only came to Godric's Hollow to cast the personality-transfer spell onto Harry and maybe get rid of the parents. He accepted Lily's offer because it amused him to have Lily sacrifice her life when he wasn't going to kill Harry anyway.
Voldy came to kill Harry, and never gave up on that intention. He pretended to accept Lily's bargain because he was Evil, and pretending to accept bargains and then breaking them is what evil people do. However, there was some hidden magic that auto-cast the Unbreakable Vow spell without Voldemort knowing. Voldemort tried to kill Harry, which broke the vow he had made to Lily, insta-killing him. Harry was Horcruxed and Voldemort's soul survived in the Horcruxes in a way relatively similar to in canon.
In canon, the explanation is that sacrificing your life in order to save someone else has actual magical force (the events of book 7, in which this effect works for Harry even though he did not actually die, imply that this effect is tied up with a person's intent to sacrifice their life, rather than their actual death). Thus, if a wizard knowingly and willingly sacrifices their life to save that of another, that other person gains a measure of magical defense, which was the reason that Voldemort's first attempt to kill Harry rebounded. I'm not sure how or whether this will be changed in MoR; if you use the intention interpretation, then it doesn't seem to horribly contradict any of the established contra-canon facts.