My point is that if you don't have some preexisting information, you quickly reach a point where you're just staring at a TV with no purpose. No new questions or observations are going to pop into your head. Whereas if you have some specific things in mind, it's going to take you longer to observe those things, and the longer you stand in front of the TV actually paying attention to it, as opposed to drooling while watching the same scene from your Lord of the Rings DVD for the twentieth time in a row, the more chances you're going to notice something out of the ordinary, even if it's not something that's on your list.