How does "How to Transform" end, and what has the narrator learned by the end?

Near the end of the summer, the narrator's coach, Slim, offers to buy a hot dog and a Coke. The narrator realizes Slim cannot really afford to buy these things, so he politely says no. Later, when he tells his father what happened, his father is disappointed in him and tells him, if someone who has nothing offers to give you something, you take it. After reflecting on what his father has said, the narrator writes about Dante in his essay: when someone who is mostly quiet offers you advice, you should take it. The narrator has learned that when someone sacrifices to give you something, you should recognize just how valuable what you are getting truly is.