There's a lot to learn when it comes to the system they employ. In a way, the QB actually makes the decision as to which play they will run, based on what they see across the line of scrimmage. That's not saying they change the play, it means they have to choose one of the options associated with the play. A QB needs to process all of it, and make the decision quickly. He must also understand what every player out there is going to be asked to do, when he makes that call.
This is the point where the rubber meets the road for a college QB. No matter how much raw talent they have, the coaches need to be confident that the guy will make the right call, or the system will implode.