Supernatural, Season 2

Molly:
I don't understand how a guy like this can turn into that monster.

Sam:
Well, spirits like Greely are like wounded animals. Lost... in so much pain they... that they lash out.

Molly:
Why? Why are they here?

Sam:
There's some part of them that... that's keeping them here. Like their remains, or unfinished business.

Molly:
Unfinished business?

Sam:
Yeah. It could be revenge. It could be love, or hate. Whatever it is, they just hold on too tight. Can't let go. So they're trapped. Caught in the same loops. Replaying the same tragedies over and over.

Molly:
You sound almost sorry for them.

Sam:
Well, they weren't evil people, you know. A lot of them were good, just something happened to them. Something they couldn't control.

Dean:
Sammy's always gettin' a little J. Love Hewitt when it comes to this. Me, I don't like 'em. And I'm sure as hell ain't makin' apologies for 'em.