There is enough evidence to support a hypothesis that the characters all started as caricatures, but such a hypothesis would be moot. I don't know how many revisions Noel went through with his script, but there is not a sharp edge to be found in any of the characters, nor their various interactions. This is all the more impressive given the pushing and pulling the script does with the characters and, in the case of Grover and Jane, the evolution we see. I imagine that Noel could tell you about each character's childhood in depth, and it would all ring just as true as what we see in the movie. Call me a simpleton, but that is a "good movie trump card" in my book.
Like most glowing artistic criticism, listening to my tone will set you all wrong on the movie. It isn't perfect, and a big part of why I like it is undoubtedly that I relate to it so well. But maybe it is worth watching.
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Tonight, I saw "The Trip", which was hilarious. I can't remember the last movie I saw that was as funny as it is. And it, too, rings of truth foremost in its conversations and relationships and it too leaves narrative form (even further) in the background - good for it. But the real bonus was Steve Coogan's dream that Noah Baumbach wanted him to star in his next movie. Now, I can't claim that Michael Winterbottom was thinking what I am thinking. But, I am thinking that Steve Coogan's character in The Trip is an older, British version of Grover - cynical, listless, intelligent, talented.
I suppose that we all fit on some great tree of archetypes and sub-archetypes, and whatever you call it when someone you just met reminds you of someone you used to know, but you can't quite put your finger on what it is about them.