By the way, the above time Terutz answers it very well, to an extent.
One way of putting the question is that if my knowledge of your choice is like Syag mentioned, due to knowing you very well, then, perhaps unbeknownst to yourself, you aren’t really deciding. So instead we are answering that the prior knowledge is only based on the choice.
There is only the issue of saying that in some way, you are affecting Hashem ChV since you changing what He knows or knew, and it’s as if in some way He had to wait for you to find out. This is where the Rambam comes in, telling us that His knowledge is not gained the way ours is.
edited for clarity