In the play "Twelfth Night" Shakespeare shows how anyone can be blinded by love and act so impulsively to satisfy their appetite for love, that often they fall in love with a faade rather then the person behind the disguise. Also Shakespeare also shows how people are apt to ignore the evidence that disproves the disguise they have fallen in love with. Almost all of the characters in "Twelfth Night" fell in love with a disguise; I will detail the confusing relationships and disguises used in the play to show the blindness of love.
Olivia is easily the largest victim to love and disguise. Olivia quickly falls in love with Viola, who is disguised as "Cesario". Olivia realizes how far from manly "Cesario" is, he has very effeminate features and lack of any facial hair. Olivia disregards these features and believes that he maybe just a eunuch. Olivia is obviously blinded by love in this case for a number of reasons; she ignores the evidence that points to "Cesario" as actually being a female. Second she justifies his features as him just being a eunuch, but never really addresses the issue that she is in love with a eunuch who of course would never be able to sexually please her or give her children. Whether "Cesario" is really a woman or if he is a eunuch, the love that Olivia has is futile and unrealistic. When Sebastian, Viola's brother, encounters Olivia for the first time, she believes that this is "Cesario" and gains the courage to ask for his hand in marriage. Once again this is evidence of how blinded by love Olivia is, she believes that Sebastian is the person she is in love with when really he is a stranger and she disregards his comments about not knowing her. Later in the play, when Viola reveals herself, Olivia's reaction to this is very calm for she has married the disguise that she has fallen in love with.
Antonio, the friend of Sebastian, falls deeply in love with Sebastian after caring for him for so long after the shipwreck. Antonio never considers the thought that Sebastian may not love him back because Antonio is so focused on his love. Antonio is unrelenting with his love towards Sebastian to the point that he risks his life by accompanying him to Illyria, where he is a wanted man. The disguise that Sebastion wears is not one he deliberately puts on, but one that Antonio places on him to disguise any signs that his love may be one sided. Finally the disguise is violently torn away when Antonio learns that Sebastian has married Olivia so abruptly.
Malvolio is deeply in love with Olivia, whom he is a servant to. He has often received negative signals from her, but he does not pay attention to them. Malvolio receives a note that Maria left for him as a trick and Malvolio quickly believes that it is from Olivia to him. Malvolio is so content with the idea of Olivia finally showing her affection for him that he doesn't question why, in the note, she asks him to act so oddly or hear the snickering of the pranksters watching him.
There is also the idea that Olivia's power and beauty causes many to fall for her. Orsino, Sebastian, Sir Andrew, and Malvolio all are in love with Olivia, but it may just be the shallow love for money and beauty and not one for true love that causes this. Sebastian agrees to marry her without ever knowing her prior to that moment, but he immediately falls in love with her beauty and doesn't second-guess the marriage acceptance. Malvolio is probably enticed by the notion that he is subservient to Olivia, she is rich and powerful and to marry her would raise him from this status. Orsino although already rich and powerful probably is interested in marrying an equally powerful person to increase his wealth and power. And finally Sir Andrew who is also enticed by the acquisition of money and power through marrying someone who is also beautiful. Olivia does not use this as a disguise however her suitors never look past this faade to see the real Olivia. Although I make no inference that this faade hides an evil monster I just say that the men never look past it because they like what they see and ask for nothing more.
Orsino may be the only exception to my thesis because he looks past the disguise of "Cesario" and falls in love with Viola regardless of her dressing as a boy. When Orsino learns the "Cesario" is really Viola his actions though are pretty hasty. Orsino gives no second thought to the fact that he has fallen in love with a woman while she was disguised as a man. Orsino is mostly happy because now his love can be accepted and Viola, who also loves him, can happily marry.
In conclusion the characters in "Twelfth Night" are very quick to fall in love with the surface disguise of a person rather than looking any further and questioning their love. Also the characters often disregard any evidence that destroys the disguise they love. Although this practice may often be very shortsighted in the time frame of the play most of the characters are happy at the end.