A simile is a literary device that compares two things using the words "like" or "as." Similes make writing more interesting because they help the reader create a more vivid picture of what the author is trying to say in the poem, short story, or novel. One example of a simile in "The Bass, The River, and Sheila Mant" is when the narrator is discussing Sheila noticing him:
Finishing, I would boost myself up onto our dock and glance casually over toward her, but she was never watching, and the miraculous day she was, I immediately climbed the diving board and did my best tuck and a half for her and continued diving until she had left and the sun went down and my longing was like a madness and I couldn’t stop.
This simile compares his longing for her to a madness. It's effective because it allows the reader a better way to understand how desperate the narrator is for Sheila's affections. The reader sees that he is infatuated with teenage "love" for her, and he can't stop the feeling - it's like a sickness. This example helps set up the major conflict of the story - should the narrator cut the line of the monster bass he accidentally hooks, or should he maintain his fish-free date with Sheila? His teenage obsession with her complicates his decision and rivals (and eventually overpowers) his love of fishing. This simile helps the reader to better understand the narrator and his emotions.