Macbeth's downfall lies mainly in "Vaulting ambition, which o'erleaps itself / And he gains his object, and it is the last." But he still has his ambition which pushes him towards his eventual downfall. Having obtained the crown, he is further ambitious to keep it in his own family. Surely, just one more murder gives him all he wants, but it goes on.
The audience's initial impression of Macbeth, based on the captain's report of his valor in the battle, is immediately complicated by his fixation upon the witches' prophecy. Macbeth is a noble and courageous warrior, but his reaction to the witches' prophecies emphasizes his great desire for power. Macbeth immediately realizes that the fulfillment of the prophecy may require conspiracy and murder on his part. He allows himself to consider taking such actions though he is not resolved to do so by no means. Instead of resolving to act on the witches' claims or simply dismissing them, Macbeth takes himself into a kind of thoughtful stupor as he tries to work out the situation for himself.
In the following scene, Lady Macbeth emerges and drives the hesitant Macbeth to the beginning of his downfall. She goads him by questioning his manhood and implying that he is less than a man. Just as Lady Macbeth proves to be the antithesis of the idea wife, Macbeth proves to be a completely disloyal subject. In his first lengthy soliloquy, he reveal that he is unable to quell his desire for power. Macbeth shows his awareness that he may be initiating a cycle of violence that may eventually destroy him. Macbeth is not a good man at this point in the play, but he is not yet an evil one; he is tempted, and he tries to resist. But Macbeth's resistance, however, is not vigorous enough to stand up to the witches and his wife's ability to manipulate him.
After killing Duncan, Macbeth's fear comes true as his downfall becomes real. Before the crime, it takes Lady Macbeth's steely sense of purpose to push him into the deed. After the murder, her powerful personality begins to break up, leaving Macbeth's to increase alone. Thus, he swings between first of fevered action, in which he plots a series of murders to secure his throne. At first, he feels that he must kill his friend Banquo and his his son Fleance because of Banquo's knowledge of the prophecy and to prevent its second part of becoming realized. Yet, his downfall reaches its height with the murder of Macduff's family. It marks the moment in which Macbeth descend into utter madness killing neither for political gain nor to silence an enemy, but simply out of furious desire to harm.
After this, the audience knows that nothing can stop Macbeth's murder spree except his own death which the audience now waits. Only with Macbeth's demise, a kind of moral order can be restored to Scotland. Macbeth ceases to be a sympathetic hero once he makes the decision to kill Duncan, so by the end of the play, he has becomes so morally repulsive that his death comes as a powerful relief. Only with Malcolm's victory and assumption of the crown, Scotland and the play itself can be saved from chaos engendered by Macbeth.
However, Macbeth displays a kind of reckless bravery as his enemies surround him and drag him down. In part, this stems from his fatal confidence in the witches' prophecies, but it also seems to drive from his return to where he has been most successful; the battlefield. As a great tragic hero, he never contempplates suicide; "Why should I ... die / On mine own sword." Instead, he goes down fighting, bringing the play full circle; it begins with Macbeth winning on the battlefield and ends with him dying in combat.