Final answer:
Victor breaks his promise to the creature due to fear of creating a race of monsters, damaging their relationship and steering the creature towards revenge, which drives the plot's advancement and tragic trajectory.
Step-by-step explanation:
In Frankenstein, Victor breaks his promise to the creature because he realizes the potential consequences of creating a companion for it, fearing they might produce a race of monsters. Victor's action permanently damages their relationship, as the creature feels betrayed and vows revenge, directly contributing to the tragic events that follow. Their interaction is pivotal in developing the plot and intensifies the novel's themes of ambition, consequence, and isolation. Victor's change of mind illustrates his internal conflict and corresponds with the broader narrative of a man struggling with the impact of his overreaching quest for knowledge, much like the ancient Greek story of Icarus. This crucial moment where Victor destroys the creature's would-be companion amplifies the creature's feelings of abandonment and propels him into a vengeful path, which becomes integral to the unfolding storyline and its climax.