Final answer:
Marji makes a surprising philosophical comment about how convictions change over time, shifting from open hills in youth to hidden caves as people age.
Step-by-step explanation:
The surprising philosophical comment that Marji makes to her parents reflects a nuanced understanding of human nature and the complexity of personal growth. While there are several instances where Marji shares her thoughts, one significant philosophical musing occurs when she notes that convictions change with age, suggesting that at eighteen they are hills from which we look, but at forty-five they become caves in which we hide.
This illustrates Marji's contemplation on the rigidity of beliefs as people age, indicating a depth of thinking that is unexpected given her youth.