The speaker pictures their thoughts as a river and floats along it, unable to steer. Along the way they bump into hard, sharp rocks, though a few spots are softened by green moss, so the journey isn't entirely harsh. Garbage drifts alongside them, which suggests the constant clutter of unwanted thoughts that never stops arriving.
Then the poem turns to a bigger question. We're told we can be whatever we want, but the speaker wonders who we are underneath the pressure to invent ourselves. "Did I make myself?" gets no reply from the rocks or the trash, and the speaker simply floats on, jaw clenched, which hints at tension and quiet resignation. In the last lines the river becomes a mirror, and looking at oneself hurts: the speaker is cut on its edges, leaving a crimson trail behind. The mood is anxious, reflective and a little bleak, ending on uncertainty rather than any answer.