This one specific psychological need or mechanism most often drives characters' motives and thus plot events and twists. How do we see this specific need or mechanism at work, and in what ways, in "Bridge of Snow"?
We see compensation at work in "Bridge of Snow" in how the goatherd needs to fill the "hole" of losing his god - one he longs for to compensate for his vulnerability to the cold and need for lasting beauty amid perhaps fatal hardship. This is paralleled by Arin's need to hear and then apply this fable to his fears of death, punishment by the gods, and loss of his older sister.
We see instigation at work in "Bridge of Snow" in how Arin, eager to replace his younger sister in his stepmother's affections, tells an elaborate story about a lone goatherd in the mountains who learns that his sister has broken the goat pen's gate. Arin enjoys seeing his family members clash, believing that "their rubble will build [his] castle."
We see machination at work in "Bridge of Snow" in how Arin's mother modifies a traditional fable to lull her son into sleep. She knows that her husband will continue to hide his looted gold from her if he believes that she's not, above all, an "effective" mother. She has overheard him plotting to trade this son for yet more wealth, but only if the boy is "brought up to be fierce like fire."
We see frustration at work in "Bridge of Snow" in how Arin, jealous about his younger sister's status as the family favorite, tells an elaborate story about a lone goatherd in the mountains. Notably, this goatherd is himself frustrated that the god of the wind is slowly making him deaf to music.