I can't speak for Calvinism specifically, but the way I always looked at it was that if God knew everything, and specifically the future, then surely he knew who was going to Heaven or Hell in the end, which meant I ultimately had no say in the matter because the results were known since the beginning of time. I couldn't make a decision that would cause my fate to deviate from what God already knew would be the case.
I don't know if this is what Calvinists believe, but one way I've seen it handwaved is that while God knows what you'll do in the end, it's not an excuse to be a terrible person because you don't know what the end result will be, but if you're a terrible person you're definitely going to Hell. Better to try to be good and hope you were one of the chosen before time began who makes it, whatever circumstances may conspire to make that be the case or not.
These days I look at it in a different light, but with the same fundamental message. I believe in a deterministic universe (and to be sure this is almost religion since all of our evidence points to the contrary..), which means that I don't actually make decisions at all. When I decide to do something, it's for a reason. I'm writing this post because I want to share my opinion and it's relevant. I just ate something because I was hungry. I just committed some code to Git because it's my job. You can chase these "becauses" all the way back to the beginning of time and to whatever resolution you choose, and if you set them up in the same fashion and let them unfold then they should come out to the same conclusion, right? And all of my future actions are going to be based on my current situation and previous experiences, so what choice do I really have?
Of course, you can try to inject quantum mechanics and uncertainty into the mix, but I feel like that would at best add randomness, and randomness isn't really making decisions either, is it?
The only way around this that I see, which some religious people probably do ascribe to, is that there really is some supernatural element that imparts free will through quantum fluctuations that appear to be random. But... well, if you believe that God knows everything and the future then we end up back at square one of my post.