How Original Does Your Book Have to Be?
Ideas always come from somewhere, and in a sense, nothing is completely original. Your work tends to look like other works in your day, with similar stories, themes, and genres. But it is still your own ideas that need to stand.
One should never borrow a piece of another’s published material for their own work. No piece of intellectual property should ever be grabbed by the writer or artist.
Ideas worth holding onto would come to your own mind: C.S. Lewis saw an image of a faun walking in the snow with a parcel and umbrella for years, and the Spanish artist Joan Miro saw things in his mind or on the ceiling, and jotted them down. Of course, I’m no expert in all the ways people come up with ideas.
There is nothing new under the sun; Romeo and Juliet and Cleopatra share almost the same exact plot, but at least it was Shakespeare’s own work and not copied from someone else’s, necessarily. Although I once researched that Twelfth Night did have older forms written by someone else. However, originality might not have had the same meaning back then.
Your book should not be a mere copy of real life if it is fiction; if so, no one will take your characters seriously and you’ll be in danger of accidentally using a real name in place of the “code” one. All parts of your book should be tied to the main purpose of it, its thesis; no character or setting or word or deed should be superfluous to the purpose, and from there, I think you won’t have to be afraid of not being original.