Endurance is a nearly spiritual thing in this book. One fights with the spirit and not with the body. A good portion of the text deals with the idea that the body and mind are separate. When Santiago's left hand cramps, he looks at it as if the hand has a life of its own, separate from his inner or spiritual or mental life.
The old man does not want to end his life now in failure. He is concerned that if he does not catch the fish, he is going to lose. There comes a point when all he cares about is not losing.
There is a definite move to make us identify with Santiago in his struggle and to sympathise with his character. At the end of the story, we cry with Manolin at Santiago's resilience, strength and fortitude and how he suffers a tragic failure in losing his fish to the sharks. And yet what stands out of this story is the way that he is able to pick himself up and carry on, determined to carry on fishing and determined to carry on dreaming.
If you didn't worry about Santiago--an old man in this battle against a fish--it wouldn't matter if he caught it or not. As mentioned above, that's one indication that this is good literature. Most of us would have trouble connecting with him on almost any other level. We may not be old or men or fishermen or live in Cuba or see the sea and the fish in it as friends and brothers or whatever, yet we feel Santiago's pain and we know what it's like to work really hard for something we badly want. We also know what it's like to work hard to achieve something only to have it kind of evaporate or diminish before our eyes. So, in actuality, we have a lot in common with this old fisherman from Cuba. And we care what happens to him. And that's good.
I think part of what makes the struggle between the old man and the marlin so epic in proportion and engrossing is the extreme odds he faces. Yes, he's older; yes, he's alone; yes, he's exhausted. But such is the nature of such classic battles. We should worry about him. Such an emotional attachment to a character during such a struggle is part of what makes great literature!
The old man and the fish both do what they do with dignity, without crying, and with courage. That's part of what Hemingway is about. Winning isn't important because sometimes you do and sometimes you don't. What is important is how you behave, that you carry yourself with dignity, behave according to the "rules." The old man loses the fish (the fish that fought bravely despite its "loss"), but that is not important because he behaved "well." His strength came from his behavior, not from the results.