The Stone Wall is the image with which the underground man names the limit that the laws of nature, the natural sciences, and mathematics place on man: the impossible, before which others calm down and he does not.
In Chapter III, the man of action, when revenge seizes him, advances like a bull with lowered horns, and only a wall stops him, before which he yields sincerely, because the wall seems to him a solution that reassures. The narrator does not yield and does not break through: "Of course I won't butt my head against such a wall if I really lack the strength to break it, but neither will I resign myself to it just because I have a stone wall before me and my strength has not been enough."
He thus separates two things the man of action joins: failing to overcome the wall and accepting it. It is the smallest form of resistance, and the only one he has. The wall returns in Chapter V, when the offense becomes fate, like a toothache no one is to blame for, and there is nothing left but to beat against it; and in Chapter IX, under the name Twice Two. In Part Two, the word appears in another sense: the decent man of his time is cowardly and a slave, and the brave ones are so only up to a certain wall.
The text leaves two readings open: the dignity of someone who does not bend to what crushes him, or the sterile stubbornness of someone who refuses a wall that remains standing.