If all the Horcruxes (and by extension the wizard's soul) are intact, the wizard is considered immortal. Splitting one's soul is considered a violation of the very laws of nature, and existence in such a form is preferred by very few, and is therefore considered Dark Arts of the most vile.
While the three Hallows actually did exist, becoming immortal from gathering the three was a misconception, as being a true Master of Death was realising and accepting the fact that death was inevitable and there were far worse things than death.
Being a horcrux simply means that Harry had a piece of Voldermort's soul inside of him. That would not grant him immortality. Harry Potter after this part he is no longer a Horcrux, Voldemort destroyed his part of the soul that resided in the boy.
But Harry didn't die, and the reason is rather simple: when Voldemort cast the killing curse, it only killed the piece of his soul within Harry, not Harry himself. Harry then saw Dumbledore in a version of King's Cross station, something that Dumbledore said was probably happening in his head.
Throughout the series, this limit is continually mentioned, and wizards who try to surpass it most often create magical disasters instead. Likewise, it is not possible to make oneself immortal unless one makes use of an object of great power to sustain life, such as the Philosopher's Stone or Horcruxes.
It depends on a persons willingness to kill someone and also the power behind the wand. To quote Barty Crouch/Mad-Eye Moody in 'Harry Potter and the Goblet of Fire', “Avada Kadavra is a curse that needs a powerful bit of magic behind it.
One reason that Harry lived after being hit by the Harry Potter Killing Curse in The Deathly Hallows is his mastery of the Elder Wand. There was a belief that obtaining the Deathly Hallows would grant the finder some sort of immortality, which is how Harry survived Avada Kedavra in the forest.
Notably, Voldemort appeared to be entirely unaware of this split, as he later created a seventh Horcrux in his quest to have six, and continued to target Harry Potter despite him now holding part of Voldemort's own soul.
Did Voldemort realize Harry was a Horcrux after he killed him?
Voldemort wasn't aware of Harry being a pseudo-horcrux because he didn't plan it, and Harry didn't know either until Voldemort “killed” him, but he actually killed the piece of soul kept in him.
How did Harry survive Avada Kedavra the second time?
Harry survived Avada Kedavra multiple times due to the protection of Lily's sacrifice and the love-based magic that surrounded him. The Elder Wand, which Harry mastered, protected him during the Battle of Hogwarts and prevented Avada Kedavra from killing him.
IT was when Harry and Hermione were on their own without Ron, and were hunting for the Horcruxes, its when Harry used to wake up with terrible headaches in themiddles of the night screaming sometimes. Hermione's research into Horcruxes at that time concluded Harry was Voldermot's Horcrux.
In Deathly Hallows, Dumbledore explains that because Voldemort used Harry's blood to regain his body, as long as Voldemort lives, Harry lives because of the weird blood protection thing that Lily placed upon Harry when she sacrificed herself.
Voldemort's death in Harry Potter proved that he never achieved his goal of immortality. He may have once been as close as he possibly could, but when he and Harry faced off at the end of Harry Potter and the Deathly Hallows, none of his Horcruxes remained.
Also, James Potter was a pure-blood. One possible theory indicates that the author of the Directory considered the Potters and other "pure-blood" families (such as the Princes, the Crabbes, the Goyles, the Moodys, and the Browns) to have some amount of Muggle ancestry.
How did Harry survive if he dropped the resurrection stone?
Harry held the resurrection stone right before he was killed by Voldemort. Even though he dropped the stone at that time he was the Master Of Death. He was in possession of the deathly hallows because the wand was his the cloak was his and then the stone was his. That is why he did not die.
The prophecy is mentioned throughout the series, however, it never exclusively mentions that Harry is The Chosen One and suggests Neville was another option. However, one theory explains why, in reality, this wasn't possible.
Dumbledore knew about Horcruxes. He knew how they were formed, what happened after that, etc. He probably got to know Harry was a Horcrux when he saw the Scar on Harry's forehead, but maybe he wasn't sure.
On confirming Draco's very much alive status, she plainly lied that Harry Potter was "dead". This action of hers was both very crucial and important, not only for Harry's survival but for Voldemort's final defeat as well, thus ensuring Harry was again protected by a mother's love, although indirectly.
Voldemort intentionally made six Horcruxes, but when he used Avada Kedavra on Harry, he unintentionally created a seventh Horcrux. Instead of dying, Lily's love for Harry created a counter 'curse' known as Sacrificial Protection and saved Harry.
Was Dumbledore raising Harry like a pig for slaughter?
In the Harry Potter and the Deathly Hallows book, Severus Snape does accuse Dumbledore of using Harry. Snape tells the old wizard: “You've kept him alive so that he can die at the proper moment. You've been raising him like a pig for slaughter!” Dumbledore does not deny these accusations, which doesn't help his case.
This would bring him into conflict with fanatical Death Eaters like Bellatrix Lestrange later in life, but Snape was almost immediately forgiven by the reborn Voldemort, because he could provide him with thirteen years of information on Dumbledore and the Order of the Phoenix.
"Tom Riddle was 15/16, young, arrogant, already evil. So so from his perspective, Dumbledore is an old man, much older than he really is. "In Dumbledore's memory he probably FELT older than he actually was, as he was in the middle of a war with Grindelwald.
