What is the metaphor? What does Hemingway’s story mean to you?

The extended metaphor in The Old Man and the Sea works like this: man vs. fish/man vs. nature/ man vs. his own nature — finding success in failure and finding failure in success. Hemingway put it this way in the story:
“But man is not made for defeat,” he said. “A man can be destroyed but not defeated.” I am sorry that I killed the fish though, he thought.
Hemingway used those words in making what he was fond of calling a “double dicho”. a saying that means almost the same thing forwards and backwards. “A man can be destroyed but not defeated.” / “A man can be defeated but never destroyed.” – Michael Dixon