Well... all i can say is that our minds are far more powerful than we acknowledge... have you ever thought about the amount of calculations that should be needed to throw, lets say, a knife and its tip enter nicely the target? Remember that we have to consider the movement of the knife, its rotation around itself, the air fricction, the gravity pull, and so... if we would put into a computer, im sure it would be a long calculation... and yet, the knife-throwers who works in circus does it without even think... and they throw the knives with such precision that sometimes they put a woman in the target, and she never is hurt.
Ok, maybe its not a very good example, but im sure you get the idea.

And if you are determinist, why does you think previsions are so impossible? Accordingly with the determinism, everything that will happen is already determined. So, why does we cant know what will happen, if its already decided?
The free will, the impredictable character of things is what makes the previsions much more difficult...


EDIT: Only now, after re-reading your post i could understand the last paragraph of it... and it will take me some time to think about... as what you said there is really well thought...