The Old Man and the Sea is the story of the conflict between one man and his ultimate goal. Santiago is a fisherman - he makes his livelihood by catching fish and selling them at market. This means the fish he catches must die so he can live. Santiago is proud of his ability as a fisherman, but he loves the ocean and deeply loves and respects the fish he hopes to catch. As he and his great fish struggle against each other, Santiago experiences deep internal conflict regarding his rights to earn a living by landing this fish as opposed to the fish's rights to continue living.
Then he began to pity the great fish that he had hooked. He is wonderful and strange and who knows how old he is, he thought. Never have I had such a strong fish...Perhaps he is too wise to jump...perhaps he has been hooked many times before and he knows that this is how he should make his fight...But what a great fish he is and what he will bring in the market if the flesh is good.
Even after catching the fish, Santiago was still filled with doubts about what he had done.
Perhaps it was a sin to kill the fish. I suppose it was even though I did it to keep me alive and feed many people...You were born to be a fisherman as the fish was born to be a fish.
The novella's premise of unity helps succor Santiago in the midst of his great tragedy. For Santiago, success and failure are two equal facets of the same existence. They are transitory forms which capriciously arrive and depart without affecting the underlying unity between himself and nature. As long as he focuses on this unity and sees himself as part of nature rather than as an external antagonist competing with it, he cannot be defeated by whatever misfortunes befall him.