Macbeth has several character flaws that combine together into a "perfect storm" that causes his downfall and tears apart his country.
In act 1, soon after the witches depart, Macbeth learns that he is now Thane of Cawdor, as they had predicted. He wonders if the other part of the prophecy, to be king, will come true. While part of him wants to believe, he is gripped by fear.
...why do I yield to that suggestion
Whose horrid image doth unfix my hair
And make my seated heart knock at my ribs,
Against the use of nature? Present fears
Are less than horrible imaginings....
Aware that fear is holding him back, Macbeth has an internal conflict with his other flaw, ambition. After speaking with the king, he begins to realize that he is taking seriously the idea of usurping his role, and worries about the black desire of his own ambition.
Stars, hide your fires;
Let not light see my black and deep desires:
The eye wink at the hand; yet let that be,
Which the eye fears, when it is done, to see.
By scene 7,...
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