“The passing game is practice and it is precision. That’s obvious,” he said in Lombardi on Football. “What isn’t obvious is the persistence: the persistence of the practice field, the persistence of the playbook, the persistence of the quarterback and receivers who must read those defenses and read them correctly, the persistence of those unsung linemen up front who must put on those pass blocks and make them stick, the persistence of the end and flanker and back who must run a route precisely to move their defender to clear an area for the receiver, and the persistence of that receiver to get clear and catch the ball.”
...
From "The Official Vince Lombardi Playbook" by Phil Barber