Why does the narrator of Chicago say that the young man has a terrible burden of destiny and that he laughs even as an ignorant fighter laughs who has never lost a battle?

The narrator of Chicago says that the young man has a terrible burden of destiny and that he laughs even as an ignorant fighter laughs who has never lost a battle to convey the idea that it's important to stay positive even knowing that you're going to struggle. Chicago was written by Carl Sandburg.