3 ideas
In a poor central Vietnamese village in the 1980s, Thiều falls for his classmate Mận and writes her poems. Mận grows close to his gentle younger brother Tường, and Thiều, unable to bear that she might prefer Tường, lashes out in a jealous impulse and leaves Tường seriously injured and unable to walk for a time.
A child can feel adult-sized emotions like romantic love, possessiveness and humiliation without the judgment to hold them, so the feeling turns straight into action before the child grasps its consequences. The damage is real, but its source is immaturity rather than malice, and the child often understands what he has done only after it is too late to prevent it.
The elder sibling experiences any warmth that parents, friends or a crush show the younger one as warmth taken from himself, even when nothing has actually been withdrawn. Because he keeps score this way, the younger child's innocent kindness reads to him as competition, and he turns resentment on the sibling rather than on the situation.