Dean and Sam in “Unfinished Business”

Dean

I'm tired, man. I'm tired of fighting who I'm supposed to be.

Sam

Well, do you think maybe you could take a half second and stop trying to sacrifice yourself for a change? Maybe we could actually stick together?

Dean

I don't think so.

Sam

Why not? Dean, seriously tell me. I-I want to know.

Dean

I just... I don't believe.

Sam

In what?

Dean

In you. I don't-I don't know if it's going to be demon blood or some other demon chick, or what, but I do know they're gonna find a way to turn you.

Sam

So you're saying I'm not strong enough.

Dean

You're angry. You're self-righteous. Lucifer's gonna wear you to the prom, man, it's just a matter of time.

Sam

Don't say that to me. Not you, of all people.

Dean

I don't want to, but it's the truth and when Satan takes you over, there's gotta be somebody there to fight him. And it ain't gonna be that kid. So, it's gotta be me.