Green Knight = Bertilak?

After finishing Sir Gawain and the Green Knight, I was left with a nagging question: How did Gawain not know that Bertilak was the Green Knight? Yes, the Green Knight is decked out all in green and may look and act a little different as per his disguise, but for Gawain to be completely taken by surprise by his true identity is hard to believe. Gawain spent days in the company of Bertilak and failed to notice anything amiss. This would lead me to believe one of two things. 1) Gawain is extremely dimwitted and is not so observant as a knight. Or 2) Morgan le Faye's magic must have been extremely powerful to completely hide Bertilak's identity behind a little green disguise. However, after weighing these two options, I've found that it's neither one nor the other; it's both. First off, Gawain is unobservant, but not in the way you'd automatically think. Back in Part II, Gawain's shield has a five pointed start emblazoned on the front. We know that the number five has many symbolic meanings. Five denotes Christ's five wounds, the five senses, our fingers, and spiritual blindness. In a way, Gawain is completely blind to Bertilak's disguise because he is not spiritually strong. His spirituality needs to be tested before he can see the light. Second, Morgan le Faye's magical powers really are quite daunting. She is described as "a mistress of Merlin" (line 2248). As the most powerful wizard in the King Arthur stories, Merlin has quite a bit of pull in that department. Bertilak even goes on to say that Morgan "guided me in this guise"(2456). Not only does Bertilak have her magic on his side, but he also has her wisdom.
So, I learned that I can't just jump to conclusions about the likelihood of a story's plot. Although the Green Knight/Bertilak grand reveal seems cheesy at first, after closer examination of the surrounding story, it works. We just have to be paying attention to the clues.