What does Viola learn about herself in Shakespeare's Twelfth Night?
If Viola did not know so already, one thing she learns about herself is that she certainly possess a great deal of gumption. To have gumption is to be resourceful and even to be aggressive. Gumption is also defined as "courage, spunk, [or] guts" (Random House Dictionary). Viola shows gumption when she first decides to bravely go to work for Duke Orsino disguised as a eunuch. We learn in the very second scene that not only has Viola just survived a shipwreck, she believes she is the only member left in her family; her father died earlier, and now she believes her brother, her remaining guardian, has drowned in the shipwreck. More importantly, she is a wealthy noblewoman and knows full well what a vulnerable position she is in with respect to being both wealthy and all alone. Hence, she resolves to disguise her identity as a noblewoman until she feels it is safe for her to disclose who she really is. A second way in which she demonstrates she has learned she has gumption is in her treatment of Olivia. Not only does she tell Olivia she is cruel to reject Orsino, she even ends their conversation by wishing a man Olivia loves will be as cruel to her as she has been to Orsino, as we see in the lines:
My master, not myself, lacks recompense.
Love make his heart of flint that you shall love;
And let your fervor, like my master's, be
Placed in contempt! Farewell, fair cruelty. (I.v.272-75)
Literally what she is saying here is that she hopes one Olivia loves will have a heart of flint, meaning stone, and that he will also hate her passion, in the same way she hates Orsino's passion. Hence, since Viola is so bold as to make this statement to Olivia, it shows us she has learned that she has a great deal of gumption.
A second thing she learns is that she does not only have the ability to deceive but also the ability to hurt through her deception. Viola realizes this when it becomes clear to her that Olivia has fallen in love with her as Cesario. Since Olivia is in love with her when she is really a woman, Olivia will feel very hurt indeed when she learns the truth about Viola's identity. We see Viola disclose her revelation about deception and disguise in her lines, "Disguise, I see, thou art a wickedness. / Wherein the pregnant enemy does much" (II.ii.26-27).