The speaker of this short poem feels shut away. The title, "Inmate," suggests a prisoner, but the "hole" in the second line could just as easily be a grave, a pit, or a low place in the mind. Either way, the speaker has been left alone there and has "gone good and dull," as if isolation has worn down every sharp edge. The word "good" is a little ironic, since being dull sounds more like a loss than an achievement.
The middle lines point to a kind of learned wariness: caution is now "used against any door," so even a way out is treated as a threat. The ending turns strange and almost darkly funny. The speaker seems to have "fell down dead" in another time, yet is "pretty well" now. The poem suggests someone who has survived something that felt like dying and settled into numb, careful calm. The mood is flat, quiet, and uneasy, with a dry humor that keeps it from self-pity.