The issue is simple, Volki, if every choice you make or thought you have is truly just the outcome of a long string of events acting each other to eventually act on and influence you, then when you are asked to choose left or right, it is a trick question as whether you go left or right doesn't actually have a single thing to do with you or what you think. You only had the option of following the path that was predetermined by factors beyond your control.
Eh, I wouldn't go that far. The choice has everything to do with how you "think" as long as you define thinking as the physical action your brain takes to make decisions. The thing is that how your brain thinks is via chemical reactions and electrical pulses.
If I ask you to pick a number between 1 and 10, your brain will choose one. But that number choice is just a mental construct represented by a specific neural pathway in the brain. Your neurons took that pathway as a response to specific stimulation and memory. But remember memory, like the rest of your brain, is just chemicals. Chemicals interact in specific ways.
So the choice you made was actually made by your brain (duh). But your brains behavior depends on its neural pathways. Its neural pathways depend on its chemistry. Its chemistry depends on its chemical and physical history. It's history depends on physical laws. Essentially you are just the product of what has happened to you.
That's not to say that your thoughts and actions are not your own or are not important, it's just that your brain
couldn't have reacted differently given the same state and stimulus. Just because your brain chemistry determines your choices doesn't make them any less significant. At least that's what I like to believe.
Ah, posts during writing. Oh well I already typed it up.