Act 1 Scene 2 notes
Viola, too, has lost a brother, but her situation does not allow her to mourn for him for seven years, abjuring other company, as Olivia plans to do, so she realistically plans a way to survive.
Viola's first reaction is to serve Olivia, and only her unwillingness to allow any suit prevents her.
Since identity is always one of the main themes of Shakespeare's plays, the way that the main characters judge the character of others is important. The smart characters know that it is not always possible to tell by a person's outward appearance his inner virtues, but Viola chooses to trust the Captain and is not misjudging.
For propriety's sake, Viola must disguise herself to find a place at the Duke's court, so her masquerade as a young man is a necessity. Unlike Rosalind, who at first takes on her disguise as a kind of game and an opportunity to satirize men who swagger and boast, Viola does not enjoy her disguise.