Responses
I think the broken ribs were actually from beatings he received, not from him trying to stay alive. And then I think he was beating himself more as self flagellation (which ironically also was good against the hypothermia) because he felt he had disappoint sam myeong and needed to repent so that sam myeong wouldn't hate him
You’re right, the broken ribs make more sense if they came from the beatings. No way a kid could hit themselves hard enough to self inflict that.
I think that pounding on his chest actually saved Changgyeon from hypothermia. Repeated physical activity can generate enough heat to protect vital organs. The downside, though, is that he broke several ribs in the process. He’s unbelievably strong to think of something like that without any prior knowledge.