Concerning Hemingway's The Old Man and the Sea, I would suggest that determination is not the only theme in the novel. It may be the dominant theme, but it is not the only theme.
When reading the work, we find situations that concern loyalty and friendship. We find issues that raise the subject of poverty. We find individualism. We find isolation. The human condition is examined in this novel.
We also see Santiago represented as a Christ figure.
Santiago is a complex character in a complex situation. Much more than just his determination is present in his story.
I'm not sure what you mean by when can such a question be asked. Your question is appropriate here. I would certainly suggest you go to the link for The Old Man and the Sea Themes, though, for further reading.