I think I can improve on the Pizza analogy. Here is the concept behind the pizza analogy:
“There are many different paths to the future. Hashem knows where we will end up and which path we will take. We don’t know where we will end up. We may deviate from the correct path for us and end up with a different future. Does this make sense? “
A better analogy might be playing chess against a grandmaster. You can move the pieces any way you chose, but the outcome is known in advance. (You are going to lose.)
If we make the game more complicated to reflect the reality of how complex our world is, then the answer becomes clearer.
Now imagine that you are playing three dimensional chess with a cube shaped chess “board”. Imagine further that since there are six sides to this chess “board”, you are playing against 5 other people – each of them with their own set of pieces. Most humans would not be able to see one move ahead. Imagine that one of the players can analyze the position of each player and see the consequences of all players moves and counter-moves five moves ahead. That player is going to decide the outcome, even though each of the other five players is free to move his pieces any way he chooses.
I have found that most people find this analogy satisfying enough to allow them to move on. I hope it does the same for you, RationalFrummie.