I would argue that one of the most powerful moments in this novella which shows Santiago's dignity in the face of failure is when he returns to port after he has lost his catch to the sharks, and yet manages to shoulder the mast and take it back home, in spite of his feelings of complete exhaustion and tiredness and defeat. Consider how he is described as he steps on land once again:
He unstepped the mast and furled the sail and tied it. Then he shouldered the mast and started to climb. It was then that he knew the depth of his tiredness. He stopped for a moment and looked back and saw in the reflection from the street light the great tail of the fish standing up well behind the skiff's stern. He saw the white naked line of his backbone and the dark mass of the head with the projecting bill and all the nakedness between.
Note the way that the skeleton of the fish is a symbol for Santiago's failure. The "nakedness" of the fish is paralleled by the metaphorical nakedness of Santiago, as he returns, defeated. However, he still resolutely carries his mast back to his shack, in spite of his exhaustion and the weight of the mast, showing tremendous dignity in the face of his suffering and failure.