How is resilience is presented through the poem Invictus written by William Ernest Henley?

Resilience, or the speaker's "unconquerable soul," is presented in this poem as standing firm against the onslaught to which it is subjected by life. Henley uses the metaphor of night, "black as the pit," to suggest that the speaker may feel lost and isolated, and yet he thanks the "gods" for the fact that his soul, even in this situation, is "unconquerable." Without even the promise of light, only "the Horror of the shade" beyond the darkness, the speaker's resilience is such that he is "unafraid," even in the most seemingly dire circumstances.
It is clear, too, that attempts have been made to conquer the inconquerable. The "bludgeonings of chance" and the "fell clutch of circumstance"—both vivid, near-tangible metaphors—have assailed the speaker to the extent that he is figuratively "bloody," and yet he does not bend under the blows, remaining "unbowed." The language is violent, creating a sense that resilience of the soul means withstanding a relentless barrage from all sides.
In the final stanza, the speaker seems to summon his courage and conviction, giving an indication of how he is able to maintain such resilience. The parallelism—"I am the master of my fate, / I am the captain of my soul"—emphasizes the speaker's self-reliance, which seems to be the key to his endurance of the "night" he describes.