the road trip with no predetermined destination, revisited

So I have road trips on the brain.  Back a while ago, I mentioned that I would like to go on a road trip with no predetermined destination, with the caveat that I did want to have some kind of ultimate goal or at least idea of a goal in mind for somewhere on down the line.

Brian said this made him sad, because there IS a predetermined destination. My thought was, yes ultimately you're aiming for somewhere, but that doesn't mean you have to go STRAIGHT there, hence it's an unplanned road trip! Same thing, right?

Brian said that you're supposed to just go and 'see where the road takes you.' I have no idea what that means.

No. Seriously. The concept is unfathomable. How do you decide where to turn?

Apparently, I have nary a spontaneous bone in my body.

How do you decide where to turn, when you're on a spontaneous road trip to who-knows-where?