Okay, so I’ve been meaning to respond to this for awhile, and I’ve just totally neglected it. I’ve read the same foreword and I think I share a similar appreciation for Neil Gaiman, and it’s been awhile since I’ve read it. Did he present it as a ‘problem’, this feeling that a writer is subconsciously (or consciously) borrowing from another work? I ask because I’ve never regarded it as a problem, but more as a reality (which I think you do, too, as evidenced by your last paragraph). We are inherently influenced by the stories we hear or read – news, books, short stories, novels, you name it – and I don’t think it’s a real expectation for any writer to be totally original.

Sure, there are always going to be more unique story concepts or presentations, but I can assure you that this concept is still influenced by something else.

Now, on to your question at the end of it. Many things will always differentiate you from your models, particularly if you are a “sit-down-and-write writer.” Your stories will still have your own style, your own prose, your own dialogical tendencies, to differentiate you. Theoretically, you could read a book and copy the style in your own, but I think that’d be even more tiresome and difficult than actually doing the writing yourself. Even then, it’s not plagiarism; it’s kind of a relearning. Though immoral (to yourself, mostly, I’d suggest), I doubt it’s illegal to mimic a writer’s structure.

The below is loosely related, not directly
Plagiarism is DIRECT copying, DIRECT stealing of ideas and even words.

Example of plagiarism accusation –> someone sued J.K. Rowling because she was writing a story about kids who go to a magic school and also take a special train. She lost, as I understand it, because it was implausible for Rowling to be familiar with her work. (Rowling has been sued by more than a few people).

Example of plagiarism accusation with an end–> A romance novel a la Harlequin had a scene with ferrets (or some such rodents) copulating, taken directly from a scientific text. The original writer sued to have it removed and won.