Final answer:
Macbeth is initially skeptical of the witches' predictions because the idea of becoming Thane of Cawdor and the king seems completely unbelievable. However, his skepticism begins to falter when he is indeed made Thane of Cawdor, aligning with the prophecy. This fuels his ambition and ultimately leads to moral conflict and his downfall.
Step-by-step explanation:
Initially, Macbeth is skeptical of the witches' predictions because they seem implausible and beyond the realm of reality. When he first hears the prophecy that he will become Thane of Cawdor and then king, Macbeth is confused because the Thane of Cawdor is still alive and well, and the possibility of becoming king is not something he can conceive of as realistic. The text, "But how of Cawdor? the thane of Cawdor lives, A prosperous gentleman; and to be king Stands not within the prospect of belief, No more than to be Cawdor," highlights his disbelief. However, when Macbeth is given the title of Thane of Cawdor shortly after the witches' forecast, his doubt begins to wane, as indicated by his aside, "Why hath it given me earnest of success, Commencing in a truth?" Macbeth's initial disbelief transitions into a conflict between his moral compass and his growing ambition, fueled by the witches' prophecy and Lady Macbeth's manipulative encouragement.