The full quote reads, “In my stars I am above thee; / but be not afraid of greatness: some are born great, some achieve greatness, and some have greatness thrust upon 'em.” What the imposter Olivia is saying is that even though by birth she ranks above Malvolio, he should not be afraid of her greatness. She goes on to explain that people achieve greatness in many ways: by birth, by works and by random circumstances. She then lists a series of absurd actions that Malvolio should perform to be worthy of her. When Malvolio does so, the real Countess Olivia thinks he has gone insane and locks him up. While the phrase “be not afraid of greatness” is self-explanatory, when taken in the context of the play, it suggests a snobbish pretention. It emphasizes the difference between true greatness and ineffectual attempts at the appearance of greatness.