Sebastian Afton's poem is about a person who shuts everyone out and ends up completely alone. The opening line, "so close yet so far away," sets up the main tension: he may be physically near the people around him, but he can't be reached. The "ocean" that now stands between him and his friends is a metaphor for emotional distance, something far bigger than a simple gap.
The walls are the heart of the poem. He built them to protect himself, and they worked so well that even his family couldn't get through. Now the protection has become a trap. The speaker seems to watch him with sadness, noticing how the thing meant to keep him safe has cut him off from comfort.
The mood is quiet, lonely, and heavy. The final lines, where he cries and no one knows, hit hardest because the pain is hidden. Note that the poem writes "know one" where "no one" is meant, which is likely a slip, though the meaning is clear.