One of the themes of Twelfth Night has to do with the extreme behaviors of what Shakespeare equates with insanity in love. One manifestation of this insanity in love is love at first sight. The theme is supported by the Malvolian subplot in which Malvolio is tricked into looking mad and is then imprisoned during which time his persecutors attempt to drive him mad. Since this theme is important to Twelfth night, extreme behaviors abound.
First, is the previously mentioned treatment of Malvolio, which is extreme in the extreme and which was inspired by his own extreme behaviors. Malvolio is guilty on two counts of extremism. For one thing, he expresses the Greek tragical concept of hubris, which is a mixture of excessive self-confident arrogant self-pride. It is true that as a steward to a countess, he has attained a great position of trust and prestige for a commoner, but he overdoes his sense of accomplishment and self-worth. For another thing, he has secretly fallen in love with Countess Olivia who employs him and makes himself ridiculous by muttering sweet love nothings to her in his imaginings, which are unfortunately overheard by his antagonists making him prey to their cruel jest.
The general social order of the time period of Twelfth Night both requires and allows for extreme behavior from women in extreme circumstances. For instance, Viola finds herself in an extreme circumstance after the ship wreck. On one hand, she believes she has lost her twin brother to a death at sea and is overcome with mourning. One the other hand, she has lost the protection of her male escort and is now a gentlewoman traveling in a strange place alone.
The second circumstance forces her to an unorthodox extremity in that she disguises herself as a male and takes employment as a male page to Duke Orsino. In comparison to Viola's circumstance is Olivia's. She too is in mourning for her deceased brother but social order permits her to commit to a bizarre extremity of mourning for seven years with weeping daily. Furthermore, in this social order, people seem to habitually fall in love at first sight: Viola with the Duke; Olivia with Cesario/Viola; Sebastian with Olivia. And people act in the extreme by giving love irrationally as is the case with Duke Orsino for Olivia.