Um...well, yeah, he actually did. That is the whole point of tennis. Get inside your opponent's head, make him doubt himself, make him go for the lines. Novak being the best returner in the game puts extraordinary pressure on his opponents. They know that simply rolling the ball in isn't good enough, so they try to go for more, and make mistakes, double fault etc. That is what doubt does to you. You start serving well, balls come back with interest, close to the lines, and you say to yourself, "Jesus, what do I have to do to win a point against this guy...I need to serve harder, go for the lines"...That is when 1st serve percentage starts going down, and the more it goes down, the more you start to panic. That is what happened to Nadal and so many other players against Djokovic. He gives you nothing. He makes you doubt yourself, your own game.
I couldn't have explained it better myself. Bravo.