1. Lily's Sacrifice: Harry's mother, Lily Potter, sacrificed herself to protect him. This act of love created a powerful magical shield around Harry, essentially deflecting the killing curse.
2. The Love Protection: The Killing Curse, *Avada Kedavra*, is a spell that cannot be blocked by physical means. It relies on the intent and power of the caster. Lily's love for Harry created an invisible barrier that the curse couldn't penetrate.
3. The Bouncing Curse: This shield created by Lily's love didn't completely stop the curse. It rebounded, leaving a faint trace of the curse on Harry and causing Voldemort to lose his physical form.
Therefore, the curse didn't *backfire* in the sense of having the opposite intended effect. Instead, the curse was weakened by Lily's love, which ultimately saved Harry's life and made him a Horcrux against Voldemort's will.
Here's a summary of the key points:
* Lily's sacrifice was the key: Her act of love was the deciding factor in the curse's failure.
* Love protection: The curse couldn't penetrate the shield of love created by Lily's sacrifice.
* The curse's residual effect: The curse rebounded, leaving a trace on Harry and causing Voldemort's physical form to be destroyed.
* Harry as a Horcrux: This accidental connection between Harry and Voldemort is a crucial plot point throughout the series.
The curse backfiring on Voldemort was a pivotal event in the Harry Potter universe, shaping the entire narrative and making Harry the "Boy Who Lived."