Many writers, however, far from borrowing or seeking to be "influenced," are desperately afraid of inadvertent influence to the point of paranoia. Since every good idea has already been used, getting too anxious about such chance resemblances is a waste of time.
Here's my rule: Any idea you really like that absolutely works for your story is your idea, no matter who else might have used it before. The only limitation on this is what the audience will stand for - if you end your novel with the hero standing before a fire and the only way the ring gets thrown in is because someone else bites off his finger and then falls in, well, your audience is likely to be a bit disgusted - the resemblance is too close, the source way too well-known. Only if your intent is humorous can you get away with it.
You should not be penalized for having read widely, however. If your story has elements that you recognize as being similar to a book by someone else, so what? As long as it's your own story, and those motifs feel important and true within the context of your work, they're your ideas now.
(O.S.Card. Uncle Orson's Writing Class. Lesson 7 - On Plagiarism, Borrowing, Resemblance, and Influence.)