Looking over it again, this jumped out at me:
It is important to understand that a diegetic identity and a movie character are fundamentally different structures. The movie character is an external entity interpreted by the spectator, and thus it can have properties that the watcher could not have invented herself. A movie character may have quicker wits and broader vocabulary than the spectator has. Role-players need to use rule systems and distanced, descriptive playing styles to portray such characters: instead of telling a good joke, a tabletop role-player might just describe that her character tells a good joke, and perhaps even roll a die to justify the goodness of the joke in the game frame.
Another difference is that while characters of the static media are presented in the context of a story world, role-playing characters are presented in the context of a game world. Goldilocks is defined by her adventure: It is difficult to imagine her in another story. The context of the narrative provides Goldilocks with her Goldilocks-like qualities. For the players of role-playing characters, the world full of opportunities and potentials is the significant context, and much more central than the story.
EW: I find a lot of Hollywood movies [take great characters and put them into situations of conflict], but they fail in ways that I find very similar to the operation of a heavy-handed GM or an excessively "thespy" player endowed with shared narrative authority. Dumb, inexplicable motivations, illogical plot twists, hammered theme.
Clash Bowley: If the characters have dumb, inexplicable motivations, that's not great characters there [...]. Great characters have clear, understandable motivations.
EW: True, it's a tautology. The thing is though that characters can start out great only to be betrayed by the exigencies of plot and stereotyped expectations. Whether that means they were never really great, or that they didn't have any greatness until fully revealed in the course of the story is perhaps a philosophical question when it comes to static fictions that can be revised before release. With RPGs, character has to precede plot IMO.
In short, while the old saying "Character is plot, plot is character" (F. Scott Fitzgerald) is arguably true for static fiction (though perhaps not, when we consider intertextuality and other elements of reader reaction), the identity doesn't hold for RPGs, except possibly if the participants decide to import the concept.