In Twelfth Night, Shakespeare uses the 16th century Festival of Twelfth Night to demonstrate the strange association of love to madness. Nowhere is this more pronounced than in the "notoriously abused" situation Malvolio is caught in. Fabian and Toby, with Maria and Feste, aggravate Malvolio's secret and over-reaching feelings of love for Olivia and egg him on to behavior that makes him look like he has become "distracted" (mad), then lock him up in prison thereby proving his madness while simultaneously attempting to convince him of his madness.
Orsino opens the play by drawing an analogy between music and love, with the hope that an excess of music might satiate the appetite of love and sicken it so it might die. In the same scene (1.1) Orsino receives a message saying the Olivia will not allow Orsino to woo her because she will spend seven years in morning, weeping each day for her dead brother. Both these situations render love as an excess that compels the bearer of love to irrational behavior. Viola comes along and sheds some wisdom on a sounder, more stable form of love, though it too is a love borne at first sight.