Grief and guilt run through "Should've Been Me" from start to finish. The speaker is haunted by the death of someone named Daisy and wishes, again and again, that they had died in her place. Nightmares follow them through the day and night, and even simple things like breathing and walking feel like unfair privileges. The poem doesn't say how Daisy died or who she was to the speaker, so we are left with the feeling rather than the story.
The mood is raw and heavy. The language is plain, almost like a confession, which makes the pain feel honest and unpolished. The image of Daisy's body "cold as ice" in "unforgiving ground" sets her stillness against the speaker's warm, moving body, and that contrast drives the guilt. Repeating "unfair" shows the speaker circling the same thought and unable to escape it. The ending, about having "the guts to walk" while she never will, leaves us with a quiet, aching sense of loss.