I could tell that Mrs. Winterbottom was trying to rise above some awful sadness she was feeling, but Prudence couldn't see that. Prudence had her own agenda, just as I had had my own agenda that day my mother wanted me to walk with her. I couldn't see my own mother's sadness.
This quote is from Chapter 17. Both Phoebe and Prudence shout at their mother, Phoebe because she thinks she is fat, and Prudence because Mrs. Winterbottom suggests coming to watch her at cheerleading tryouts. Phoebe's and Prudence's rude and dismissive behavior causes Sal to remember an afternoon shortly before her mother left when she snapped at her mother's repeated requests to take a walk. When Sal sees Phoebe and Prudence acting in a similar manner toward their mother, Sal realizes how blind she had been to her mother's emotions and point of view. Sal puts her realization in the vocabulary of the second message, "everyone has their own agenda." Thus, she demonstrates a real understanding of the message's meaning: every person is wrapped up in their own concerns and more often than not fails to see or respond to the needs and problems of others. To Sal, people are like pinballs, flying past each other, occasionally colliding, but more often than not remaining oblivious to the small kindnesses and quiet cries for help others extend. In her reflection on the Winterbottom household, Sal also displays her understanding of the first mysterious message: "don't judge a man until you've walked two moons in his moccasins." This moment in another person's family helps her sympathize with her mother's emotions at that moment long past.