Bobby and Dean in “Unfinished Business”

Bobby

You can't give up, son.

Dean

You're not my father. And you ain't in my shoes. [Bobby looks heartbroken and Sam gives Dean a disapproving head shake.]

Bobby

[Takes out a gun and a bullet]

Dean

What is that?

Bobby

That's the round I mean to put through my skull. Every morning, I look at it. I think, "Maybe today is the day I flip the lights out." But I don't do it. I never do it. You know why? Because I promised you I wouldn't give up!