[He grunts in agreement. He hadn't realized it would color her own feelings about motherhood, but now that she points it out it makes sense.]

Right. And everybody who becomes a parent knows exactly what they're supposed to do.

[Just a bit of light sarcasm there. Only a moment later, though, he does have to concede her point.]

We owe it to him to do our best. I guess that means knowin' our limits too. We can't be his parents, but... well, I don't know about you, but I'm gonna do what I can for him.