•Why it earns a slot
Why it earns a slot: the poem the world knows as "Invictus" was never titled by Henley himself, and sits buried mid-collection next to the far more graphic, far less quoted ward poems it actually came out of.
A journalist who lost most of a leg to tuberculosis at twenty-five turned the hospital ward into verse, then buried inside it the four lines that would outlive everything else he wrote.
This distillation is written from the freely available original, which is always the better read when you have the time: Project Gutenberg.