I have no spur
To prick the sides of my intent, but only
Vaulting ambition, which o’erleaps itself,
And falls on the other.

– William Shakespeare

Macbeth, Act 1, Scene 7. Ambition is one of the strongest themes in Macbeth. In the final words of Macbeth’s soliloquy, he reveals that the sole reason for his murder of Duncan is his ambition. An extended equestrian metaphor explains that he has no other motivation to spur himself to commit regicide than ambition. Shakespeare also personifies ambition as overleaping and falling, which also foreshadows Macbeth’s downfall.