The most difficult point to take (and this is particularly true if you play a great player) is the last one. In my opinion, the main problem Federer had was psychological one stemming from wanting it too much. I think that at 40:15 he:
1) Rushed. He should have taken time to think, which would also allow Djokovic to think (putting him under pressure).
2) Decided in advance what he is going to do. He decided that he will not be passive and that he will be maximally aggressive, i.e. any ball I get, I will play as aggressively as I can. He put Djokovic under pressure, but Djokovic was up to the task (lesser player would miss passing shot). Federer should have played those points little bit more by the ear.
3) Possibly, he did not truly believe that he will cross the line (like Mirka). He panicked.
1) Rushed. He should have taken time to think, which would also allow Djokovic to think (putting him under pressure).
2) Decided in advance what he is going to do. He decided that he will not be passive and that he will be maximally aggressive, i.e. any ball I get, I will play as aggressively as I can. He put Djokovic under pressure, but Djokovic was up to the task (lesser player would miss passing shot). Federer should have played those points little bit more by the ear.
3) Possibly, he did not truly believe that he will cross the line (like Mirka). He panicked.