Quote 1
I could just drift, he thought, and sleep and put a bight of line around my toe to wake me. But today is eighty-five days and I should fish the day well.
Just then, watching his lines, he saw one of the projecting green sticks dip sharply. (2.54, 2.55)
The old man’s determination is immediately rewarded. Hemingway portrays a cause and effect here.
Quote 2
Nothing happened. The fish just moved away slowly and the old man could not raise him an inch. His line was strong and made for heavy fish and he held it against his hack until it was so taut that beads of water were jumping from it. Then it began to make a slow hissing sound in the water and he still held it, bracing himself against the thwart and leaning back against the pull. The boat began to move slowly off toward the north-west. (2.75)
The fish possesses a determination equal in magnitude to Santiago’s.
Quote 3
What I will do if he decides to go down, I don’t know. What I’ll do if he sounds and dies I don’t know. But I’ll do something. There are plenty of things I can do. (2.78)
The old man’s determination is enabled by the variety of skills he possesses.