Sebastian (believing him to be Cesario), while Orsino himself will not find out the truth about his servant until the end of the play (when he proceeds to marry her).

Meanwhile, Sonnet 130 seems to be a call for emotional honesty, rejecting the kind of poetic license and exalted metaphor through which love is so often expressed. As far as the speaker is concerned, this makes for an altogether stronger kind of love, in that it entails full recognition and acceptance of the beloved not as an idealization, but as a flesh and blood person, with all the flaws and imperfections that this entails...

The deceptiveness of appearances is a frequent theme that William Shakespeare employs. In his plays, disguises and enchantments often hide the true identity of a character or transform them into another person or type of being. Another type of misleading appearance is created by twins whose lives get mixed up. The result is frequently comedic, as when an apparent change of gender causes a person to fall in love with someone of the same gender. Closely related to disguise is a change in appearance when a person is trying to look or act like someone they are not, perhaps because they have been misled into thinking that there is something to be gained through this appearance

Twelfth Night is one of Shakespeare’s comedies in which disguise and deception are major parts of the plot. The most obvious example is the young woman, Viola, disguising herself as a man, who uses the name Cesario. This plot becomes further complicated through the mistaken twin plot device. In this case, Viola’s twin is male, Sebastian. The romantic complications ensue when Olivia falls in love with Cesario, believing he is a man. The problem is exacerbated when Sebastian’s friend Antonio gets into trouble when he interferes in Cesario’s affairs because he mistakes him for Sebastian.

Another use of deceptive appearance involves Malvolio, Olivia’s servant. Because he has an unpleasant personality, some other characters play a trick on him. They fool him into believing that Olivia would like to see him dressed very fashionably. In trying to please her, he wears an outfit that instead makes him look ridiculous.

In Sonnet 130, the speaker establishes a set of comparisons, saying repeatedly that their mistress is not as beautiful as a whole assortment of natural phenomena. For example, her cheeks are not as red as roses. At the end, however, the speaker criticizes these sorts of typical poetic analogies, dismissing them as “false compare.” In rejecting those falsities, the speaker endorses their own “rare” love for her.

Both Twelfth Night and Shakespeare's "Sonnet 130" use humor to show one shouldn't judge a book by its cover.

In Twelfth Night, the main "cover" is Viola's disguising of her gender. She poses as a male, Cesario, so that she can work for Duke Orsinio. This leads to comic confusion, as Cesario/Viola is sent to woo Olivia for the Duke, only to have Olivia fall in love with Cesario/Viola, who Olivia thinks is a man. Meanwhile, Viola falls in love with the Duke. Olivia's love is for Viola's "cover," Cesario, and the implication is that she would not have fallen in love if she had known Viola were a female. At the same time, the situation raises the question of exactly what part of Viola Olivia has fallen in love with—the surface or the soul? This provokes an even deeper question: how much does gender matter?

"Sonnet 130" pokes fun at love poetry that uses conventional language to praise a beloved's surface beauties, such as comparing one's lover's eyes to the sun or lips to coral. Shakespeare says his beloved does not have these skin-deep beauties. Nevertheless, he doesn't judge her by that "cover." Even without these exaggerated surface perfections, his beloved is to him as "rare" and worthy as any lover described with cliches.