Interesting thought about the writing of Neil Gaiman: He writes about what happens on the other side of barriers.
In “Neverwhere,” the barrier that was crossed was a social one, where Richard Mayhew notices a badly injured and he assumes lowerclass woman and crosses the line of socially accepted behavior. He takes her back to his apartment, sees that she gets the care she needs, and he ends up becoming trapped in London Below, an entire society of the dispossessed with its own rules and its own reality. In London Below, the names of London Above, from Blackfriars to the Angel Islington, take on an entirely new level of meaning and significance; i.e., there really are black friars and there really is an angel named Islington.
In the book “Coraline,” the girl of the title lives in a home where a locked door once led to an adjoining apartment. She wonders what lies beyond the locked door, and one night discovers that it is open and walks through it, into a dark parody of her own home, where an evil Other Mother waits like a spider to ensnare Coraline in her web, and where her only ally is a cat.
And now the movie “Stardust” has just come out. In this case, though full disclosure requires that I admit I have neither seen the movie nor read the book, the action begins in a town called Wall, where a young man sees a star fall beyond the wall from which the town takes its name and promises to bring it back to the woman he is courting. Once he crosses that wall, the standard rules of reality that he has lived under no longer apply.
So it goes. Gaiman is a postmodern writer, who delights in showing the other side of belief, of reality, and holding it up as a mirror to the reality we all know and experience. I suppose that for him the best trigger for a story is to see a border or a barrier, and to wonder what lies beyond it.