The task of speculative fiction is to speculate, to extrapolate, to say "what if"?

But the future has a way of turning out very differently from what we expect. In the case of Dune, Herbert's prediction wasn't just a satirical warning of what might happen if current trends were projected into the near future, but a detailed explanation of what was about to happen, and why it had to, thinly disguised as occurring in the far future.

The essay I linked to discusses this at length. The world of Dune, and of the contemporary ferment in the Islamic world, seems inevitable from today's point of view, given the historical causes for it. But before it happened, and while it was unfolding, no one else saw it coming.

That's what I find astonishing about Herbert's prescience. We all had access to the same clues, obvious ones in retrospect, and we missed it. Our ability to predict the future doesn't fail so much because of our inability to anticipate what will happen, but our inability to understand our own past, and our failure to see what is going on right before our eyes.

What this suggests is that even if a society can develop the historians, artists, philosophers and scientists that can make valid speculations about the future from our knowledge of the past, there is still a momentum to history that may override that prescience. Individual humans can foresee the future, and they can even make it happen, but they can't seem to be able to do both. Free will means we can make our own future, predestination means it makes no difference because we don't know what we're doing.