[غنوج]

I found this reasons on another site :
1-Viola, for unexplained reasons, wants to escape from the world, so she decides to pretend to be a lowly male servant. Interestingly, she takes on this new, very different identity partly because she identifies strongly with Olivia, who is a woman with a similar temperament to her own.
2-Because of her disguise as Cesario, Viola is able to make a poignant speech about love and the nature of women.
3-Having been shipwrecked and needing to find refuge, Viola disguises herself as a youth, and in a sense claims her brother’s identity, while keeping his memory alive in the process. Having lost him, she is left alone and must look to her own resourcefulness to secure her safety.

Not surprisingly, she does so, and provides us with the first of many instances of her wisdom, shrewdness and thoughtful nature -- "Conceal me what I am, and be my aid/ For such disguise as haply shall become/ The form of my intent. I’ll serve this duke" (Twelfth Night, 1.2.49-51).