You used the term predetermined there so I just want to note to others that no-free-will doesn't imply fatalism. It's not that whatever was going to happen is going to happen anyway whether you do anything about it or not. That would imply cause without an action and it's the exact opposite of what the idea of no-free-will in a deterministic universe means.

Determinism is about everything following from past events and the state of the universe at that specific moment and that the ability to have done otherwise is an illusion. So you didn't grab a chocolate bar at the checkout because it was predetermined at your time of birth that this would happen but you also didn't grab it because that's what you chose to do there and then and you could've also chosen not to grab it. No - you couldn't have. You didn't choose to be hungry, you didn't choose to notice the chocolate bar there, you didn't choose to like Snickers more than Twix and so on. Everything that ultimately led to you grabbing that specific chocolate bar was outside of your control and the fact that you did grab it means that if we rewind the universe back to that same moment, everything else being equal, you'll just grab it again, and again, and again. How could you not grab it? That's like saying 4 + 4 is 8 but it could also be 6. No it can't. It's always going to produce the same result no matter how many times you run the calculation.

We do things for two reasons: either you want to or you have to. There's obviously no freedom in having to do something but you're not free to choose your wants either.