Written in second person, the poem describes someone running flat out with no destination, no sense of when to stop, and no willingness to glance behind. The speaker watches this runner with a mix of pity and warning. The shadow in the title seems to stand for fear, or the problems in life a person would rather not face. Because it is attached to you, it keeps pace however fast you go.
The speaker's tone is steady and a little weary, as if they know how this ends. The line about others who "have been there before" suggests people who already learned the hard way that there is no finish line. The short, repeated "No" and "Not knowing" lines build a breathless, driven rhythm, which mirrors the running itself. The mood is tense and urgent at first, then quieter and more hopeful in the last line, "Until you finally wake up," which suggests that stopping and facing things is the only real way out.