Perhaps you will understand me if I give an example.
There is a number of things that I can do at 6:00. I can:
eat pizza eat a tv dinner eat nothing
Suppose that god knows that I am going to eat pizza.
It is not possible that I will eat nothing, or eat a tv dinner.
why not? because god did not know that I was going to do that that.
that means the only option is to do what god knows I am going to do, not because god made my choice, but because my choice has to be something that god knows I am going to do.