A common trope among creators is that there's nothing new under the sun, that everything we have is just novel combinations of everything that came before. Up to a point, sure: everything new often has recognizable elements of what came before swirling around within it. But to say all that's new is nothing but the recombinance of the old ... no. The new does exist. It's just awfully hard to recognize when it shows up.
People say "there's nothing new under the sun" to avoid the responsibility of confronting something actually new under the sun. They break out the identifiable chunks and point at them and say, see? I know where that came from! There's nothing new! But they gloss over the things that are new. And since the actual new thing tends to be an unclassifiable pain in the ass, no wonder they do this.
A lot of the time, the new thing isn't even wholly new, but something incrementally new in a way that causes people to blink, so that it looks like it's too new to be processed. E.g., science fiction and fantasy: the original Star Wars, which melded the graphics and hardware of the former with the form and spirit of the latter. It was such a simple and fruitful combination, and it yielded up even more when combined with modern filmmaking technique. It also took George Lucas fighting the board of 20th Century Fox every step of the way to make it come together the way he'd hoped.
Another example, less innocuous: black comedy about serial killers (American Psycho, Serial Mom). The combination seemed distasteful at first, but for those two movies in particular, it turned out to have a great deal to say about the way affluence and privilege distort the senses of both predators and prey, and the way infamy makes evil palatable. It took people with nerve and more than a little disdain for good taste to make that happen. It also took the rest of us a while to stop holding our noses and see what was actually there.
What is most required of us is to have as little between us and the thing in question as possible. Good critics try to set their egos aside — although even the best of them have trouble with that — and see the thing in front of them for what it is. Hard to do that when the thing in question pushes buttons, or doesn't connect to any experience on the critic's part. (A lot of reviews of Japanese films brought Stateside in the 50s and 60s were tainted by this kind of sniffy ignorance.) At the very least, you need to find out where the thing in question is coming from.
Those of us who make our own things, and want to strive to be original, always wonder where the really original thing first starts. From everything I can tell, it starts with whatever it is you and only you have to bring to the table — something as personalized and individuated as you can get. Folks who are mostly clever assimilators of other media may be able to create things that are superficially novel, but it's hard to make truly new things that way. Maybe that's why many entertain the feeling there's nothing new: because the new thing has to be personalized, a difficult and often market-unfriendly move. But always a worthwhile one.