"But skepticism is precisely what I've been talking to you about: the difference between believing and seeing, between believing one sees and seeing between, catching a glimpse - or not. Before doubt ever becomes a system, skepsis has to do with eyes. The word refers to a visual perception, to the observation, vigilance, and attention to the gaze during an examination. One is on the lookout."

http://www.youtube.com/watch?v=dj1BuNmhjAY