Characters
All of you! You think there’s someone just gonna drop money on ya?! Money they could use?! Well, there ain’t people like that. There’s just people like me.
— Jayne · Firefly

Behind the line May contain spoilers.
Our reading
An editorial interpretation.
Jayne treats generosity as unbelievable because he measures everyone by his own reluctance to part with useful money. The insistence moves from a claim about other people to a revealing admission about himself. His certainty closes off the possibility that anyone might act from a different set of motives.
Context reviewed