Aristotle will always have thought of it before you. But by creating a novel out of that idea you can make it original.

--- Umberto Eco, interviewed in The Paris Review, The Art of Fiction No. 197, Issue 185, Summer 2008, p. 91 (this excerpt not on the web page)

Quote in context:

An idea you have might not be original - Aristotle will always have thought of it before you. But by creating a novel out of that idea you can make it original. Men love women. It's not an original idea. But if you somehow write a terrific novel about it, then by a literary sleight of hand it becomes absolutely original. I simply believe that at the end of the day a story is always richer - it is an idea reshaped into an event, informed by a character, and sparked by crafted language. So naturally, when an idea is transformed into a living organism, it turns into something completely different and, likely, far more expressive.