Why does the neighbor say that “good fences make good neighbours” in "Mending Wall"?

The neighbor gives no practical reason for needing a wall; there are no cows to keep out, and the two properties have only trees. When the speaker questions the saying, the neighbor repeats, “Good fences make good neighbours,” echoing the belief his father passed down. So the best answer is that he is repeating what his father used to say.

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