When Santiago finally wins over the large fish, he finds that the blood trail, so far out in the water, is attracting sharks. He kills the first one with his harpoon, but it gets stuck and he loses it. The loss of his harpoon and the knowledge that more sharks are coming almost serves to break Santiago's will; it is almost better to have never won the fish if he will not be able to show it off:
It was too good to last, he thought. I wish it had been a dream now and that I had never hooked the fish and was alone in bed on the newspapers.
"But man is not made for defeat," he said. "A man can be destroyed but not defeated."
(Hemingway, The Old Man and the Sea, Google Books)
Using all of his tricks, skills, and willpower, Santiago fights off the sharks, finally making it back to shore with nothing but the skeleton and head of the fish. Despite his low mood, and the fact that he has lost all the meat of the fish, Manolin realizes that he has not lost anything; in fact, with the other fishermen seeing the skeleton, Santiago has won back his respect and his reputation. His hard work was destroyed, but he proved his self-worth again, and so Santiago himself has not been defeated. It is possible that he even dies after the end, but this doesn't even matter; Santiago beat back old age, caught a huge fish, and then beat back the sea and the sharks, refusing to give up. The persistence of willpower that Santiago shows proves that he can be destroyed in body, but not in mind.