The initial quotation of Count Orsino's words in the opening scene are interesting because it gives us a very good glimpse of the character: he's moody, passionate and a bit self-centered:
If music be the food of love, play on;
Give me excess of it; that, surfeiting,
The appetite may sicken, and so die.
....Enough! No more.
'Tis not so sweet now as it was before.
This character sketch is confirmed by his remarks about Olivia; after all, look how he talks of first meeting Olivia: There is not too much about her, it's all about himself:
That instant was I turn'd into a hart;
And my desires, like fell and cruel hounds,
E'er since pursue me.
VIOLA: Caught between her love for Orsino and Olivia's attraction to her, she blames her crossdressing for her troubles. This is a recognisable cultural trope. There are myriad of crossdressing comedies featuring similar moments of conflict.
"Disguise, I see, thou art a wickedness,
How will this fadge? my master loves her dearly;
And I, poor monster, fond as much on him"
In addition, Viola's description of Feste is a good definition of a Shakespearean Fool:
This fellow is wise enough to play the fool;
And to do that well craves a kind of wit:
For folly that he wisely shows is fit;
But wise men, folly-fall'n, quite taint their wit.
The Feste proves Viola's observations by teasing Malvolio who has just received what he thinks is a love letter from Olivia, a letter that was actually forged by Maria, and Feste knows this. This is important because it is the heart of the subplot that symbolizes the greater struggle Viola's roles and difficulties represent.
Why, some are born great, some achieve greatness,
and some have greatness thrown upon them.