Here's a more literal take on the question. I sometimes come up with a great sentence and wonder if it's original or whether I've recalled it from way back, source forgotten. In that case I google it and damn, it can be a line from an old film or a quote from a novel. Of course it's harder to search for the same plot point on google but maybe it works as well.

I would think that most topics have been covered before and just repackaged differently. Even great scientific inventions are based on what has come beforehand, followed by a leap. Or as Newton said, from sitting on the shoulders of giants.