[tash9]

I think what he's trying to say is that a human has limited time to analyze variations, so they would typically analyze the "best" move for a given situation.

But if you make a suboptimal move, then you are going down a path that is less analyzed and thus you are likely to have an analytical advantage.

So while the board state is well known, what your opponent has researched is not known, or partially known (since players have favorites and predispositions).