To what does the old man attribute his destruction in The Old Man and the Sea?
Santiago, while fighting the sharks, speaks the motto: "A man can be destroyed but not defeated." This refers to his inner strength, the ideal that if he commits to his fullest ability, refuses to give up, and struggles to his last breath, then he has not been defeated, but merely "destroyed." The body can be killed, but the effort remains. However, fighting the sharks weakens his body and his resolve, and when he finally gets closer to shore, with the marlin eaten down to its skeleton, he finds that it is possible to give up:
He knew he was beaten now finally and without remedy... It is easy when you are beaten, he thought. I never knew how easy it was. And what beat you, he thought.
"Nothing," he said aloud. "I went out too far."
(Hemingway, The Old Man and the Sea, Google Books)
Santiago's thought is that he simply over-committed, that he took too large a fish and let it drag him out too far into the ocean to have a prayer of returning safely. He tells Manolin "They truly beat me," referring to the mindless destruction of the sharks and his inability to save the marlin. It could be said that Santiago's hubris destroyed him, but in the end, it was just a stack of factors stronger than his will and beyond his control. Santiago's body was hurt, possibly beyond repair, but he brought back the skeleton, and so people see his achievement.
Santiago in the story The Old Man and the Sea is a fisherman, like his father was, and his father's father. He takes great pride in his profession but he has no been able to catch any fish. He travels out to sea to make one big catch. He does this and has to fight all the elements of the sea to keep his fish. Santiago returns to the land with not much more than a fish skeleton with some scraps that could be cut up and used for bait. However, he had met the struggle and had caught his fish. The other men are amazed at the length of the fishes frame.
Santiago, like the villagers, is superstitious. He believes his destruction is because he is no longer lucky. When one is no longer lucky one can not catch fish.