Quote 22
I wonder what he made that lurch for, he thought. The wire must have slipped on the great hill of his back. Certainly his back cannot feel as badly as mine does. But he cannot pull this skiff forever, no matter how great he is. Now everything is cleared away that might make trouble and I have a big reserve of line; all that a man can ask. (2.104)
The old man compares his pain to the pain of the fish; this is what allows him to see brotherhood between them.
Quote 23
The bird had flown up when the line jerked and the old man had not even seen him go. He felt the line carefully with his right hand and noticed his hand was bleeding.
"Something hurt him then," he said aloud and pulled back on the line to see if he could turn the fish. But when he was touching the breaking point he held steady and settled back against the strain of the line.
"You’re feeling it now, fish," he said. "And so, God knows, am I." (3.20-3.22)
The old man compares his pain to the pain of the fish; this is what allows him to see brotherhood between them.
Quote 24
This is the second day now that I do not know the result of the juegos, he thought. But I must have confidence and I must be worthy of the great DiMaggio who does all things perfectly even with the pain of the bone spur in his heel. What is a bone spur? he asked himself. Un espuela de hueso. We do not have them. Can it be as painful as the spur of a fighting cock in one’s heel? I do not think I could endure that or the loss of the eye and of both eyes and continue to fight as the fighting cocks do. Man is not much beside the great birds and beasts. Still I would rather be that beast down there in the darkness of the sea. (3.85)
Despite the immensity of his pain, the old man still believes that man is not capable of withstanding suffering as animals are. From here stems his respect for the marlin.