Winning the ATP Finals doesn't happen by chance and you truly need to prove you're better than the players there. Most of those players are players that have performed the best over the course of the past year so that makes the triumph even more significant.
For Mouratoglou the main takeaway was Djokovic's ability to win matches when he's not playing his best. He wrote on Twitter:
Swiatek, Kyrgios and McEnroe all react to Djokovic's ATP Finals triumph: "Absolute machine"
The most impressive thing about Novak is his ability to win without being close to his best level. He has shown it throughout the whole tournament.
Huge problem solver, huge ability to overcome difficulties and huge champion in negotiating the bigger moments in a match.