Macbeth was ultimately responsible for his own downfall. His ambition and lust for power underpin his violent actions throughout the play, though Lady Macbeth is often credited with fuelling his ambition.
The witches Macbeth initially encounters predict his future success and give scope to his ambitions. Macbeth acts on these predictions, murdering King Duncan and his sons in order to inherit the throne. Lady Macbeth continually goads and encourages him to use any means to advance, despite Macbeth's doubts and moral objections at the beginning of the play. The predictions of the witches and the encouragement of Lady Macbeth help motivate Macbeth, but he is ultimately responsible for his own actions in the play, and these actions ultimately lead to Macduff exacting revenge on him.