Final answer:
In the poem "Mending Wall," the neighbor believes that "good fences make good neighbors." The speaker questions this belief.
Step-by-step explanation:
In the poem "Mending Wall," the neighbor of the speaker believes that "good fences make good neighbors." This belief is repeated throughout the poem when the neighbor says, "Good fences make good neighbors." The neighbor holds the belief that having a wall between them is essential for maintaining a good relationship. The speaker, on the other hand, questions this belief and wonders why they need a wall at all.