Well, best I can explain it, is that at some point in some time, I existed as whole person, and that person lost their heart. And when your heart is ripped out of you with this magic, what's left behind is a Nobody and a shadow.

I'm the Nobody. I thought I knew why I was a high level Nobody, but now I'm not sure since Xehanort was babbling something or other, I dunno. I wasn't really listening.

[ That is a lie. ]