The Blindness of the All-Seeing Eye
I'm sure Sauron needs no introduction. His presence is treated in Lord of the Rings as a force of nature, an extension of a will so great and terrible that the very land fouls at his touch. Famously, Sauron's ever-watching gaze is represented in the films by the great lidless eye, wreathed in flame -- perhaps the most intimidating immobile body parts in modern cinema. I mean, look at it!
If there were a big eye in a tower, I could forgive if it could not look everywhere at once. Yet in the books, the Eye is more of a conceptual evil, a nearly inescapable searching which must constantly be run from. Even in this form, though, Sauron seems never to look in the right place. Gollum claims that "it attends more to some places than to others" (Two Towers).
In fact, if we extend the phenomenon, it is rare that we find a villain in a fantasy tale who does look in the right places or anticipates the hero's every move. Rather, it seems cheap to us as readers if the villain really does anticipate every move of the heroes -- to us, this is somehow unrealistic. Why is this?
When I first considered this question, I thought that perhaps the heroes of the story simply find a way to best the villain. There is always a secret pass, or an exposed exhaust port, or a traitorous second-in-command. Yet this explanation seemed to be incomplete: if the heroes always managed to overcome the villain's plans and overwhelming watchfulness by sheer badassery, then were they really a threat to begin with?
No, I would posit that supposedly all-seeing villains are blinded not by oversight, but by narcissism. No matter how all-seeing an evil overlord becomes, they can only be in so many places at once. In fact, as their dominion expands, it becomes less and less of a possibility for the villain to maintain utter control over their dominion. This self-defeating aspect of expansionist villainy creates the perfect conditions for an exploitable weakness. In Dol Guldur, Sauron had total control, but in all of Mordor? impossible. There is simply too much to manage, yet in his Hubris, the Dark Lord believes he himself can keep that level of total and utter control.
Perhaps this is not a groundbreaking revelation, but I feel that this realization about the consequences of a lack of trust gives credence to what otherwise would be labelled a literary trope. Blindness, then, comes not from an inability to see, but an inability to stop grasping beyond your sight. Who knows: if Sauron would have just kept to himself in Dol Guldur rather than attempt to dominate all life, perhaps he wouldn't have been cast down. Food for thought for all you future villains out there.