Why didn't Lily's protection prevent Harry's scar?

Question

Spoilers for Deathly Hallows:

This question about why Harry has a scar when Avada Kedavra leaves no trace got me to wondering. Why would Harry have a scar at all? If Lily's protection prevented Voldemort from touching Harry why could the piece of Voldemort's soul touch Harry at all? Why wasn't it destroyed on contact like Quirrell was later?

His mother died in the attempt to save him -- and unwittingly provided him with a protection I admit I had not foreseen.... I could not touch the boy. - Voldemort

-Goblet of Fire

--

Quirrell raised his hand to perform a deadly curse, but Harry, by instinct, reached up and grabbed Quirrell’s face –

‘AAAARGH!’

Quirrell rolled off him, his face blistering too, and then Harry knew: Quirrell couldn’t touch his bare skin, not without suffering terrible pain – his only chance was to keep hold of Quirrell, keep him in enough pain to stop him doing a curse.

-Sorcerer's Stone

Related:

Why does the piece of Voldemort's soul attach itself to the only living thing i.e. Harry?

Answer 1

My own understanding is that the soul-shard that escaped Voldemort's body, is not normal magic. It's not magic from this world. It's from the place where Harry would've gone, had he boarded the train in King's Cross. The afterlife?

There are other examples that come close to such magic force. For example Harry's parents during his duel with Voldemort in Little Whinging's graveyard(Priori Incancantem). Or simply ghosts and portraits. But the above examples are just imprints of the real persons while they were alive. The shard is something from outside the realm of the living. I believe Dumbledore came from that place, when he visited Harry, who was in limbo state -- King's Cross Chapter, Deathly Hallows. It's natural to think that the Voldemort-soul-shard might actually be from that place. Remember we also saw that shard incarnated as small baby, ugly one too.

Having the above points in mind, it's not so hard to imagine that the shard can possess powers greater than the ones known in the HP universe. Although rare, the love protection magic is known one. Dumbledore spoke of it as being "ancient". Rare it might be, but it seems to be known.

Then, do you know anyone in the HP universe who can speak little about what the afterlife is like? No information. The only thing that gets near that topic was Harry's discussion with Sir Nicholas. Harry confronted him after Sirius' death, to ask whether he could communicate with him somehow. Sir Nicholas rejected to have conversations in that topic.

My writing probably didin't answer your question. It merely suggests that it is possible that the Voldemort's soul piece, can have powers stronger than any known to the world of living.

Answer 2

I think that this question, which is different from what you are asking here, has the same answer.

While Lily's love made it very painful for Voldemort and Quirrell to touch Harry, that alone did not kill Quirrell (all we know is that Voldemort "left Quirrell to die" ~Sorcerer's Stone, The Man with Two Faces, although I might be wrong on that) nor would it destroy any of Voldemort's horcruxes, including the piece of his soul inside Harry.

It's possible the Voldemort's soul itself could not feel the pain, as when Voldemort was in Quirrell when Quirrell tried to touch Harry and Voldemort kept yelling at Quirrell to kill Harry while Quirrell was experiencing the agony of touching Harry. Voldemort was not acting as though he could feel the pain, so maybe the part of Voldemort's soul in Harry couldn't feel the pain living in Harry either.

EDIT: The more I think about it, the more I realize that Quirrell probably died from touching Harry, which hurt Quirrell as a living human being with a body but did not affect Voldemort's soul. That would mean the soul couldn't be hurt by Lily's protection, but by Lily's protection Voldemort couldn't kill Harry. This way it would allow that piece of Voldemort's soul to attach to Harry since the soul couldn't feel pain like a normal human body, but it couldn't kill Harry in any way because of Lily's protection. I hope that makes sense!

Answer 3

The Dark Lord could touch Harry - it was just extremely painful to.

It’s not strictly true that the Dark Lord couldn’t touch Harry, he could. Quirrell is able to grab onto Harry’s wrist - the sacrifice protection doesn’t actually stop Harry from being touched by the Dark Lord or those he possesses. The soul piece, then, also would be able to touch him.

“Harry sprang towards the flame door, but Voldemort screamed, ‘SEIZE HIM!’ and, next second, Harry felt Quirrell’s hand close on his wrist.”
_{^{- Harry Potter and the Philosopher's Stone, Chapter 17 (The Man with Two Faces)}}

It causes Quirrell extreme pain to touch Harry when possessed by the Dark Lord, but it is possible for him to do it. Quirrell wasn’t destroyed on contact with Harry. Quirrell died from a combination of the burns that he got as a result of continuously touching him and the agony it caused him.

“Quirrell rolled off him, his face blistering too, and then Harry knew: Quirrell couldn’t touch his bare skin, not without suffering terrible pain – his only chance was to keep hold of Quirrell, keep him in enough pain to stop him doing a curse.”
_{^{- Harry Potter and the Philosopher's Stone, Chapter 17 (The Man with Two Faces)}}

Furthermore, the soul piece isn’t a human body, so couldn’t get burned in the same way, and may not even be able to feel pain. The protection wouldn’t have destroyed the soul piece on contact or bounced the soul piece off of him, because all it does is cause the Dark Lord or whoever he possesses extreme pain on touching him, it doesn’t destroy them outright or prevent them from making contact with him. The sacrifice protection couldn’t do much to a split off piece of soul.