One of Shakespeare's central points in Twelfth Night is to show that appearances aren't really what they seem. Essentially, he shows that appearances can be deceptive. He shows us the deception of appearances through both Olivia and Duke Orsino being deceived by Viola masquerading as a boy. He also portrays the deception of appearances through the clown Feste turning out to be the wisest character of them all. But more importantly, he also shows that a person's beautiful exterior can hide a deceptive character or even poor and untrustworthy character. One example of a poor character being covered by a good-looking exterior is Sir Andrew who is described as handsome but is also known to be a drunkard, wasteful, and even proved to be a coward. The importance of physical appearances hiding an untrustworthy nature, which is a central point in Shakespeare's appearance vs. reality theme, is revealed in the very first act. While Viola is preparing to hide herself as Cesario, she tells the captain who saved her that she finds him to be very trustworthy, as we see in her lines:
There is a fair behavior in thee, captain;
And though that nature with a beauteous wall
Doth oft close in pollution, yet of thee
I believe thou hast a mind that suits
With this thy fair and outward character. (I.ii.50-54)
What she is saying here is that even though outward exteriors often "close in pollution," meaning hide an untrustworthy or even despicable character, she sees that his handsome looks are actually enclosing an equally handsome nature and character. This speech so early on in the play shows us that Shakespeare's central point with the appearances vs. reality theme is to show that appearances can hide deceptive and untrustworthy natures, which further shows us that Shakespeare views appearances to be far more untrustworthy than reality.