“Tell one part of your problem.” This is one of the moments in “Someday” that I love most. James is sitting with his grandmother, Nanette, “the poor man’s Kitty Carlisle Hart.” Since James can’t articulate what occurred at work, Nanette suggests that he pick one corner of the problem, and focus on that. Writers everywhere know this is the right approach. It’s the entire thesis of Anne Lamott’s “Bird by Bird.” It’s also Curtis Sittenfeld’s advice for trying times: Just attempt to do 500 words per day. The side entry. When I think of Cameron’s approach to 9/11, I think of front and side doors. Many writers chose to address 9/11 head-on: For example, there was Jonathan Safran Foer’s clumsy image of a man “falling up.” There was Susan Sontag in “The New Yorker”—opining awkwardly about courage. There was “United 93.” Cameron chooses, instead, to write from the point of view of a teenager who seems to have lost no one in the catastrophe. And yet he has been forced ...