Macbeth's most important character flaw is his all-consuming ambition. Lesser character flaws that contribute to his demise include stubbornness, being influenced by others and self-doubt. His downfall is a result of the unresolved tension between his ambition and his conscience, which battle for control over him through the entire play.
Macbeth is first shown to be ambitious. The first the audience hears of him is through the words of the wounded captain, who describes Macbeth's valor, courage and bravery on the battlefield. However, when Macbeth is met with the prophecy of being king, the audience learns that his internal strength does not match his external strength.
Macbeth is seduced by ambition, but he is also fearful and doubtful. He fears that the witches' predictions are not accurate and doubts his own power. Because of this fear, Macbeth resolves to do whatever is necessary to make the predictions come true, including the murder of his friend and the king of Scotland. He is heavily influenced by his wife, Lady Macbeth, who pushes him in the direction of murder despite the misgivings of his conscience. Ultimately, Macbeth's flaws get him into a situation that he is not prepared to deal with, leading to his death.