Miss Maudie says that Atticus has a talent, and you don't brag about your God-given talents.
Scout describes her father as “feeble.” She thinks of him as old. When a mad dog shows up in the neighborhood, the sheriff can’t make the shot in one try. He gives the gun to Atticus.
"I haven't shot a gun in thirty years-"
Mr. Tate almost threw the rifle at Atticus. "I'd feel mighty comfortable if you did now," he said. (ch 10)
Atticus takes the dog down in one shot. His children are shocked, because they had no idea he could even shoot a gun—let alone better than the sheriff.
Miss Maudie thinks that it’s funny that the children did not know that their father could shoot. She asks if they are still ashamed of him.
“…The very idea, didn't you know his nickname was Ol' One-Shot when he was a boy? Why, down at the Landing when he was coming up, if he shot fifteen times and hit fourteen doves he'd complain about wasting ammunition." (ch 10)
She tells the children that Atticus realized his talent was a gift from God, and gave him an unfair advantage when hunting. So he stopped hunting. She tells them a person in his right mind doesn’t brag about his talents.
Jem and Scout consider this, and decide not to tell anyone. Jem even says that he would be proud of his father even if he could not shoot. He says he is a gentleman, like Jem.