“I am the master of my fate; I am the captain of my soul.”
William Ernest Henley
Your quotation is from the poem "Invictus"
By William Ernest Henley 1849–1903
The poem expresses all the undersireable qualities of character, such as Selfisness and Willfulness, Self-Reliance, and Arrogance.
As testimony to that fact, we may apprise ourselves that the author of that poem was not "master" of anything. In fact, he committed Suicide.
The indications and signs are very familiar to me. The poem reflects the kind of arrogance associated with people who cannot "Let Go..." They insist upon the idea that they can do all things, without any outside (or inside?) help from a Higher Mind or Higher Power.
So, true enough to that kind of thinking, the author was so Egocentric, that his best thinking told him to just execute himself, which is ill-advised to say the least. He was not the Master of anything.
He was arguably, very spiritually sick, and thus, not quite the example of thinking and feeling that people will want to emulate.