Regular followers of this site will know that I am enamored of two quotes. The first is by John Cage (by way of Indeterminacy) when he realized his attempts to give freedom to the musicians in a performance of his design had, in many cases, only allowed them to be "foolish and unprofessional". On faced with this, he said:
My problems have become social rather than musical.
I demand two things from a composer: invention, and that he astonish me.
It took me two orders of magnitude more time to come to an understanding of the second quote than it did for me to do the same with the first one, but the insight mined from that expedition has been invaluable.
When we talk about a writer's "creativity", we often use the label wrongly. Not out of malice or even misunderstanding of his motives, but because we misinterpret the word before we ever meet his prose on the page. To be creative is not merely a matter of making things up; it's at least as much a matter of channeling what is around you, of paying attention to your world and reproducing it in a way that gives the material life and weight. This matters all the more in a story where so much of what happens is "made up" — like the far-future SF story I just finished writing, and which I hope I wrote well by paying as close attention to who was in it as what.
This is what Stockhausen meant by "invention", I think: not that we just make stuff up, but that we are able to synthesize our worldly experiences into something new while at the same time remaining faithful to their essences. What's more, to do that artfully, to do it so well that you think you're receiving something entirely new, and where the aesthetics of the delivery are at their peak — that's what he means by being "astonished". You must first do your homework in the school of the world around you, and then make your art into your term paper.
People, even self-professed neophiles, resist the new. They want the flavor of the new without having to contend with the actual new-ness of things; they want to go around the world but can't be bothered to put callouses on their hands lifting their luggage. A creator has to work very hard indeed to introduce them to something truly new, and the only way to do that most of the time is to give it a coating of the old, the familiar, the world we know and can connect with. He wants to invent, but he is compelled to invent by reworking the existing world instead of conjuring one up wholesale. Invent right, and the shock of the new combines with the familiarity of the old to be astonishing. The first is a means to the second; the successful invocation of the second requires the first.