The problem is that when polls are wrong, they tend to be wrong in the same direction. If they miss in New Hampshire, for instance, they all miss on the same mistake.
Nate SilverOne of the pervasive risks that we face in the information age, as I wrote in the introduction, is that even if the amount of knowledge in the world is increasing, the gap between what we know and what we think we know may be widening.
Nate Silver