A really good example of how a chapter moves a character forward in her inner and outer life is Chapter 46 of Laurie Halse Anderon's Wintergirls. In this chapter Lia’s dad finds her dozing on the couch and decides she needs to eat. A phone call from Lia’s friend, Cassie, now dead of her own eating disorder, prompts Lia’s dad to wonder how Lia really feels inside before announcing she will be reevaluated for inpatient care. Then the two spar hurling issues at eat other, the fight ending when Lia stuffs a sandwich in her mouth asking him if that’s what he wants. The chapter makes it really clear that the external struggle for Lia is food –will she eat? However, internally, family issues like divorce, infidelity, and attention to relationships are boiling. By the end of this chapter, Lia makes the decision to confront her father –is this all you want? me stuffing a sandwich in my mouth? Subtext: there is more to this eating disorder and we both know it.
So there is the external struggle: food, and their is the internal struggle underlying it: the unaddressed family issues. The characters challenge each other to take the next step forward in both of these conflicts.