It only takes 4 scenes for Macbeth to change from a noble warrior to a scheming traitor. Macbeth's transformation truly comes into view when he says "The Prince of Cumberland: that is a step on which I must fall down, or else o'erleap, for in my way it lies." This occurs right after king Duncan names Malcolm as heir to the throne. Macbeth realizes that the chances of him becoming king have just dropped dramatically, he must either give up here or take Malcolm out of the picture.