Answer:
From The Merchant of Venice, Shakespeare recounts the story of a young lady whose father was concerned about who would get married to his daughter Portia.
He decides that he wants a young man who would be able to judge objects from their inner thoughts and beauty, regardless of how the exterior is. So, he organizes a lottery and the winner would get married to Portia, in spite of what Portia wanted.
Lottery for Portia's destiny refers to what her father devised in his will whereby the suitor who would choose the correct casket would marry Portia.
It prevents her from the right of voluntary choosing by making everything a game of luck and not particularly who Portia wants to get married to.