He obviously didn't ever hear or read about Normandy. Or about the German disaster at the outskirts of Moscow the previous winter. Germany made the classic blunder of believing they were invincible (or at least acting like it) based on Hitler's Ideology of German superiority.
Additionally, he doesn't realize that the US was pretty much the only people fighting on two fronts at the same time, Europe and Pacific. Now, I don't know if he's looked at the globe lately, but Pacific was a pretty big theater. And the Japanese were tough fighters, often fighting until the last man had fallen, something rarely seen in warfare.