When the old man first encounters the large fish, what is his concern?
When the old man first encounters the fish, he is afraid that he will not be able to pull the fish into the boat. He does not succeed in pulling the fish into the boat. He then worries that the fish will snap the fishing line and he will lose his prize fish. He therefore allows the fish to pull him and the boat. At first it is a matter of pride with the old man, not losing the prize marlin, then ultimately it becomes a test of his endurance and ability to survive the long struggle with the fish.