In "The Bass, The River, and Sheila Mant", the narrator asks out Sheila Mant, an older teenage girl on whom he has a massive crush. Because he isn't old enough to drive a car, he offers to "drive" them to their destination via canoe, and, once on the boat, his fishing line inadvertently hooks a huge bass. The narrator must choose whether he reels in the bass or not, complicated by the fact that Sheila says the following quote about fishing pretty early in the story: “I think fishing’s dumb,” she said, making a face. “I mean, it’s boring and all. Definitely dumb.”
Of course, the main reason the author has Sheila say this is to set up the conflict and eventual decision that the narrator must make, but what does it tell us about Sheila as a person? We don't get the feeling as readers that Sheila has much experience at all fishing; in fact, she spends most of her time lying out in the sun. This quotation shows us that she's opinionated and pretty quick to judgment. She's not curious about fishing at all; she doesn't ask any questions about fishing. It shows us that she's not curious at all about the narrator: he clearly knows much about fish as he shared, "showing off", that they were Micropterus salmoides. She obviously does not care about his interests and is self absorbed in her own thoughts and opinions.
Why? Why is it important that Sheila be an unsympathetic character? It's important because the narrator and the readers learn a lesson from his mistake! Why should he have cut the huge bass, something he's been searching for all summer, something he has immense passion for, for Sheila Mant - a girl who doesn't care about him in the least? This valuable lesson could only have been learned if Sheila wasn't worth the sacrifice - and she most definitely wasn't.