I once explained this to someone like this: Suppose you were to sit down at length with [insert favorite sports hero here, I'd pick Brett Favre just for fun]. He is probably one of the worlds experts on how to read a defense, what the correct throwing form should be, what exercises to do in the off season, what qualities to make for a good wide receiver, etc.
Now imagine you ask him "Who is going to win Texas vs. Alabama this year" Is he more qualified to answer that than pretty much anyone you will probably meet in your whole life; yes. Does all of his expertise in other areas help in making that decision; yes. Is the guy going to do statistically better than a coin toss? Probably not. We don't need to "rethink quaterback theory" or "throwout freshman textbooks" because of this though as people seem to be fond of claiming.
Now imagine you ask him "Who is going to win Texas vs. Alabama this year" Is he more qualified to answer that than pretty much anyone you will probably meet in your whole life; yes. Does all of his expertise in other areas help in making that decision; yes. Is the guy going to do statistically better than a coin toss? Probably not. We don't need to "rethink quaterback theory" or "throwout freshman textbooks" because of this though as people seem to be fond of claiming.