Any sane normal person knows that, even those who doubt him out of fear and insecurity. Novak has said it many times himself. The major change in Novak hasn't been physical, it has been mental. Actually, the less he thinks on court the better he plays. It happens to extremely intelligent people who can't act because they think too much.
Agreed. In most professions, thinking is critical, but in sports, the less you think the better. Whenever a player says he/she was "in the zone", what they really mean to say is that he/she plays instinctively, without thinking, and pulls of all the shots he/she can think of without making any errors. Player usually has to think when things are not going his way, when he is forced to re-evaluate his tactic/game-plan. Thinking too much on the tennis court is not a good thing usually. It results in tight, nervous play and produces too many unforced errors. I'm not saying that players can never allow themselves to think on the court - indeed, sometimes it is necessary - but the need to think on the court is usually a symptom of things not going according to plan, and the sooner the instinct kicks in (after thinking/changing the tactic) the better.