Pain actually has a lot of objective parts to it. There are real chemical and mechanical processes involved. You could even argue the subjective part might be smaller than people think. Mindset can change the experience, but different people might just have different "pain functions" to begin with.
Same idea with hunger and weight gain or loss. Hunger is a biological process. You can push through it, but people also experience it differently because their actual hunger mechanisms differ, not just because they "interpret" it differently.
I don't care about the objective parts; the chemical and mechanical processes would have been exactly the same if it had been Lisa's lip that was bruised and bleeding instead of my own, or the lip of another boy halfway around the world, but it wouldn't have mattered to me in the same way.
Same idea with hunger and weight gain or loss. Hunger is a biological process. You can push through it, but people also experience it differently because their actual hunger mechanisms differ, not just because they "interpret" it differently.