In this rally between Djokovic und Raonic we can clearly see that even the pros have a hard time recovering to the ideal position every time. The following graphics will show you that the ideal position to strive for, the middle of the opponent's best possible shots is not always easy to reach. 

After a serve to the T Djokovic waits for the return slightly to the right of the center line.

Djokovic hits the shot crosscourt to the opponent's forehand and finds himself exactly in the middle of the opponent's next possible shots.

After pulling Djokovic off the court Raonic finds himself in perfect position to cover either one of Djokovic's best options.

Djokovic hits the ball crosscourt to Raonic but finds himself far from the ideal position as Raonic makes contact with the ball.  Raonic could easlily force Djokovic with a down the line shot but decides to play back towards the middle.

Djokovic returns the shot towards the middle.  Raonic runs arund his backhand and could play to either corner as Djokovic finds himself exactly in the middle of the angle between the best possible shots. 

Roaonic decides to hit an inside in forehand and ideally he should have moved to the left of the line, but instead he remains to the right and slightly out of position.  

Djokovic hits crosscourt and recovers towards the middle.  As Raonic makes contact he has one leg in the middle of the andgle.

Raonic hits crosscourt pulling Djokovic off the court and at the same time remaining in an ideal position. 

Djokovic's crosscourt shot reaches Raonic before he is able to recover to the ideal position.  Now he may be in trouble!

Raonic's down the line shot is not good enough to force Djokovic and now he is the one who is out of position.