See the free will sequence: problem statement, solution. You do determine what happens, but you do that as part of physics, which could as well be deterministic as well, with your decision being determined by that part of physical world that is you. The decision itself, while it's not made, is not part of current-you, but it's determined by current-you, and it is part of the physical world (in the future of current-you), where current-you can't observe it.