Which event in shakespeare's twelfth night triggers the series of incidents related to mistaken identity?

In Shakespeare’s Twelfth Night, the event which triggers the series of incidents related to mistaken identity is when Viola disguises as a man and work in Orsino’s court where she is mistaken for her brother, Sebastian. Sebastian is also mistaken for Viola. These cases are common in Shakespeare’s comedies. 

Epistrophe and anadiplosis because they both mean a repition of a word