It is the night of Halloween, 1981, in a house in the small town of Godric's Hollow, and the events which are unfolding are soon to become famous - despite few of the details being known. Let us examine some of those details more closely.
Lord Voldemort casts the killing curse, and his already damaged soul begins to tear. The curse strikes home, ripping James Potter's soul from its body; his life is snuffed out.
Shortly afterward, Lord Voldemort casts the killing curse again, and the tear in his soul widens. The curse strikes home, ripping Lily Potter's soul from her body; her life is snuffed out.
Mere moments afterward, Lord Voldemort casts the killing curse once more - and a piece of his own soul rips free, to be carried along with the curse. The curse strikes the protection of a desperate mother's sacrifice and rebounds upon its caster, jarring the infant Harry Potter's soul loose from its moorings.
The rebounding curse strikes home, ripping the remainder of Lord Voldemort's soul from its body, and somehow destroying that body in the process (a matter worthy of some attention on its own).
The loose fragment of Voldemort's soul, seeking an object to house it as other such fragments have already been housed, embeds itself within the first thing to hand: the body of Harry Potter.
Harry Potter's own soul, recovering something like a normal equilibrium, returns to its proper place - but with the fragment of Voldemort's soul already in residence, there is not, quite, enough room.
It settles in anyway, but due to the lack of space, cannot quite fit entirely back within Harry's body.
As a consequence, Harry will go through life with his soul extending just slightly beyond his body, and somewhat less securely attached than is usual.
What effects this may have on him, on his magic, and/or on those around him is undetermined; the answer to that question is left as an exercise for the reader. (Or, as the case may be, the author.)
(I originally came up with this as a possible explanation for a super!Harry idea - which I'll post eventually, once I manage to write it up to my own satisfaction - but it could be applied as an explanation for many other things than the one I designed it for, and could serve as the seed of a fair variety of stories.)
Lord Voldemort casts the killing curse, and his already damaged soul begins to tear. The curse strikes home, ripping James Potter's soul from its body; his life is snuffed out.
Shortly afterward, Lord Voldemort casts the killing curse again, and the tear in his soul widens. The curse strikes home, ripping Lily Potter's soul from her body; her life is snuffed out.
Mere moments afterward, Lord Voldemort casts the killing curse once more - and a piece of his own soul rips free, to be carried along with the curse. The curse strikes the protection of a desperate mother's sacrifice and rebounds upon its caster, jarring the infant Harry Potter's soul loose from its moorings.
The rebounding curse strikes home, ripping the remainder of Lord Voldemort's soul from its body, and somehow destroying that body in the process (a matter worthy of some attention on its own).
The loose fragment of Voldemort's soul, seeking an object to house it as other such fragments have already been housed, embeds itself within the first thing to hand: the body of Harry Potter.
Harry Potter's own soul, recovering something like a normal equilibrium, returns to its proper place - but with the fragment of Voldemort's soul already in residence, there is not, quite, enough room.
It settles in anyway, but due to the lack of space, cannot quite fit entirely back within Harry's body.
As a consequence, Harry will go through life with his soul extending just slightly beyond his body, and somewhat less securely attached than is usual.
What effects this may have on him, on his magic, and/or on those around him is undetermined; the answer to that question is left as an exercise for the reader. (Or, as the case may be, the author.)
(I originally came up with this as a possible explanation for a super!Harry idea - which I'll post eventually, once I manage to write it up to my own satisfaction - but it could be applied as an explanation for many other things than the one I designed it for, and could serve as the seed of a fair variety of stories.)