Discuss existentialism with reference to the novel The Old Man and the Sea.
It is important to first consider a couple of the basic precepts of existentialism. Essentially, the existentialist protagonist seeks meaning and order in a chaotic and meaningless universe. Similarly, the existentialist protagonist struggles with his own sense of alienation and isolation in order to define him or herself.
With these tenets in mind, it becomes quite obvious how these things readily apply to Hemingway's "old man" and the novel as a whole.
There is no reason or meaning to the old man having lost his luck at fishing; there is not sense or order or justice in the sharks taking his catch. Yet through the crucible of these experiences, the old man's character is revealed. Hemingway chooses to render the existential dilemma of alienation and isolation quite literally by having the old man first ostracized and then set adrift, alone, for three days in his skiff.
Though the old man does not, perhaps, find meaning and order--as exists in his beloved baseball box scores--he does seem to find an inner peace that will stave off his sense of isolation and alienation.
Existentialism is a philsophy that suggest that man has all control over his fate and the path his life will take. However, in The Old Man and the Sea, Santiago works hard, and still has no result for his work, being fishless for 84 days. I believe this part of the book is contrary to the beliefs of existentialism. But later, although Santiago is old, and should be weak from lack of food and sleep, he still manages to catch the marlin that is bigger than any he had ever seen.
*this is strictly my opinion and is in no way professionally backed. I do hope that you will at least consider my answer.