The answer is 'by not fulfilling expectations'. The other options don't really surprise the reader, and if the plot is going into one direction, and then what you'd expect to happen doesn't actually happen, you are surprised, and the element of irony is achieved.
<u>Lady Macbeth fears that her husband does not possess the personality traits that are necessary to achieve his main goal</u><u>: </u><u>to ascend to the throne</u><u>.</u> In other words,<u> she is worried that her husband is too kind to do what it takes to become king</u>, which is murdering Duncan. Moreover, in the play, she is the one that convinces Macbeth to do whatever is necessary to take the throne. Lady Macbeth is also the one that plans Duncan's death and calls her husband 'a coward' when Macbeth tells her that he should not kill Duncan.
I think the answer would be: How great human beings are.
Sorry If I'm wrong
