Do you believe in free will?

[Angrboda]

I don't really believe in free will the way most people do. I mean, I know I can control my body, but it feels like my actions are pretty much predetermined by my nature. The way I put it is: "I am the helmsman of by body, but certainly not the captain".

I know what you mean. Every morning, within 5 minutes of getting up, I have to take a dump. I suppose I could try to resist it but what is the point of that? Eventually peristalsis will triumph.

Here's a better experiment. Get stoned and try to reason yourself out of having the munchies, after all, it's just the cannabis talking.

Or stay up late and choose not to feel sleepy.

But a more pertinent question would be, given:
a) I believe incorrectly that I have free will and act accordingly;
b) I believe correctly that I have free will and act accordingly;
what observational differences will there be between a and b?