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Critics argue that this is the first example of Macbeth's ambition showing itself. Before the assassination, Macbeth in a personal reflection admits "the assassination[will be due to]vaulting ambition which o'erleaps itself" (1.7.2,27). This quote implies that the assassination of King Duncan will be due to ambition. This quote is an excellent example of excessive amounts of ambition because Macbeth realizes it is his vaulting ambition that grows exponentially or "o'erleaps itself" time after time (1.7.27). One can clearly see Macbeth knows that this train of ambition will never halt; in fact, it may lead to Macbeth committing more worse crimes or acts against humanity. However, this vaulting ambition inside of Macbeth may even let him attempt to remedy his mistakes later. This theme is implied very briefly, later, in the play. The brothers, Donalbain and Malcolm, are suspected of committing the assassination due to their fleeing of the crime scene; Ross, not knowing who committed the crime, explains the negativity of excessive ambition saying " 'Gainst nature still! Thriftless ambition, that wilt ravin up/ Thine own life's means!"(2.4.6) .
Although, Ross believes it is the brothers' ambition of becoming rulers more quickly that leads them to this horrible deed, this quote perfectly describes Macbeth's situation. Macbeth goes against nature and kills his King-the man who gave Macbeth his career, his life, and his trust. Ross blames the acts on ambition. The reader can see that Ross means to imply that the motif behind this assassination was extravagant and wasteful ambition, which caused unnatural acts of cannibalism making the sons' kill the person that gave them birth. In Macbeth's case, Duncan did trust Macbeth like his son. The prospect of going against someone that thinks of you like a son is daunting. To actually commit this act of cannibalism due to excessive ambition proves that this quality lead to his doom.
