College scouting is as much art as it is science. The best analogy I've ever heard is one describing college admissions: deciding who to draft isn't comparing apples to oranges; it's comparing apples, oranges, pears, bananas, etc., while trying to decide which one, when fed to a cow today, will produce the tastiest steak two to three years down the road.
As a case in point: consider Chad Jackson v. Greg Jennings. We see Chad Jackson as a bust, and Greg Jennings having success in Green Bay. Unfortunately, though, the Pats don't have a crystal ball, so they can only work with the information they had at the time. Yes, in retrospect, they made a mistake, but you can't make the argument that "they should have known" back then that Jennings would be better; the information they had simply did not lead them to that conclusion. [And, I might add, there's no way of knowing, e.g., that Jennings wouldn't have had even worse injuries in Foxboro than Jackson did.]
