In the beginning of the play, Olivia is mourning her brother who has recently died, after her father died. Olivia is very depressed and said that she will be mourning them for seven years; she does not want to leave her house or see any other people. Olivia changes throughout the play by becoming in love with Cesario. In the end of the play, Olivia ends up marrying Sebastian, who she thinks is Cesario (Viola), when it is really her twin brother. Even though in the beginning Olivia says she is done with all men, she ends up getting married, which shows her character’s change. Although, Olivia's mourning could have just been an excuse so she would not have to see Duke Orsino or Sir Andrew. 

Why, then, build me thy fortunes

In this quote, Sir Toby is talking to Sir Andrew about how to win over Olivia's love. Sir Toby is telling him to fight Cesario, because if he does, Olivia will love him. Toby says that women love men with honor and fighting skills, and that if Sir Andrew hurts Cesario he will have both of those things. This quote shows that Sir Toby is either dumb, or that he is not really in support of Sir Andrew, and that he really wants to humiliate him. I think that Sir Toby is not really in support of him because he knows that Sir Andrew does not know how to fight but he also knows that he is too dumb to say no to one of his suggestions. Also, if Sir Toby really is trying it shows his lack of knowledge of Olivia and love. There is evidence of this when Sir Toby believes that just because Sir Andrew could injure Cesario, that it means that Olivia will love him instead, which is false.