Viola is the focal point of the drama and its subsequent development. She is at the front and center of just about everything that happens in the play, providing the catalyst for the most important action. It's established right from the outset that Viola is a highly intelligent woman. It is this characteristic of hers that allows her to transform herself into Cesario and maintain this cunning disguise without being detected. She's also a fiercely independent woman, taking charge of forging her own identity, which transgresses the boundaries of what's considered acceptable in the society she inhabits.
Being an outsider in Illyria means that Viola isn't subject to the misguided perceptions that bedevil the natives. She's much more practical, more grounded, more down-to-earth, less prone to the dictates of emotion than both Orsino and Olivia. That doesn't mean that Viola doesn't possess a romantic streak in her soul; it's just that it's tempered by a certain practicality. Even so, Viola still has a strongly romantic element in her character, which, combined with her undoubted wisdom, intelligence, and practicality, gives her a better understanding of love and all that it entails. This, combined with her adoption of two conflicting gender roles, allows Viola to teach Orsino and Olivia the true meaning of love from the perspective of both a man and a woman.