The last two lines of the poem of Carter's PTSD flashback read,
"A brother in a band alone.
With his unknown unknown unknown."
This resonates with the famous dishonest speech of then-Secretary of Defense Donald Rumsfeld on February 12th, 2002 about the lack of evidence of weapons of mass destruction in Iraq. The full quote is, "Reports that say that something hasn't happened are always interesting to me, because as we know, there are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns - the ones we don't know we don't know. And if one looks throughout the history of our country and other free countries, it is the latter category that tend to be the difficult ones."