One of the first things Black Dog does after we are introduced to him is throw a steel knife on the table for Moon Shadow. He warns Moon Shadow that knives are necessary in America. This is ironic because Black Dog, after all, is the only character who threatens to use a knife against Moon Shadow. Black Dog is also the character who is killed with a knife to the throat near the end of the book. Black Dog clearly believes that violence is necessary to defend oneself, but we see his knife and sword usage as definitely on the offensive side. The general trend is that Black Dog chooses violence.
The author Laurence Yep gives us plenty of clues that Black Dog is bad news. His name, for example: black dog. Specifically for Dragonwings, where the dream is to be in the air and to take flight, being a dog is not exactly a winning animal. Dogs are confined to the land and definitely can't access the sky. Compare Black Dog with Robin, for example. Black Dog's inability to fly, whether literally or metaphorically, however, is his own doing. Bitter-hearted and resentful at working manual labor in a foreign land when he lived like a prince in the Middle Kingdom, Black Dog takes out his anger on the world by instigating violence or trying to escape through drug usage. One more word on his name: you know the obnoxious saying "it's a dog-eat-dog world"? Well, yeah. Black Dog is only looking out for himself.
Of course, Yep suggests that the saddest thing about Black Dog is that he doesn't have to be a lone wolf. He could easily choose to contribute to the brotherhood that exists in the Company. Instead, he turns to the false and corrupt fraternity of the Sleepers, which is, let's face it, a gang. Black Dog is the character who shows us how lonely and alienating it is to feel different and separate, to feel like one does not belong. Transplanted from his lifestyle in China, he doesn't like the reality he finds in America. And who can blame him? But he could reach out and realize he is not alone in feeling different and scared. His father, Uncle Bright Star, clearly cares a lot for him, covering his debt and not following through on his "why I oughtta"s.
Maybe the saddest thing is that Black Dog could be part of a dream, the dream of the Company and even of Dragonwings. After all, when the Company arrives to help Dragonwings fly in Chapter 12, Uncle, Lefty, Hand Clap, and White Deer are all part of the success of the dream, even if they themselves do not work on the airplane. In other words, Black Dog could be part of the dream of flight, but he instead actively works against his kinsmen by stealing their funding. It's scary to make yourself open to other people, to make yourself vulnerable; but Black Dog shows us that it's far scarier not to.