The story is this: Two neighbors - in New England, naturally - meet at a given time to repair the stone wall between their two properties. The wall may have been damaged by the freezing and thawing of the ground underneath it or the damage might have been done by thoughtless hunters, but now there are gaps that need to be mended.
As the two talk, we see two philosophies about walls. One neighbor opines, "Good fences make good neighbours." But the other asks a very pertinent question: "Why do they make good neighbours?"
And he goes on:
Before I built a wall I'd ask to know
What I was walling in or walling out,
And to whom I was like to give offence.
Something there is that doesn't love a wall, but there's no persuading his neighbor.
by Robert Frost