After Atticus kills the mad dog with a single shot in Chapter 10, both Scout and Jem are dumbfounded. Miss Maudie, a witness to the incident, immediately remarks, "Well now, Miss Jean Louise, still think your father can't do anything? Still ashamed of him?" This is an obvious reference to the children's complaints that Atticus, who is older than many of their peers' fathers, doesn't do many of the things that other fathers do. (For instance, Scout complains, in the beginning of Chapter 10, that Atticus is "feeble" and doesn't smoke, hunt, play tackle keep-away, drive a dump-truck, or do other things that other children's fathers do.)
With these complaints in mind, Miss Maudie proceeds to tell the children that their father's nickname was "Ol' One-Shot," a nickname he acquired because of his excellent marksmanship. The children, still in a state of disbelief, wonder why Atticus never told them he could shoot, and Scout says, "Wonder why he never goes huntin' now." In a very telling statement, Miss Maudie replies:
If your father's anything, he's civilized in his heart. Marksmanship's a gift of God, a talent--oh, you have to practice to make it perfect, but shootin's different from playing the piano or the like. I think maybe he put his gun down when he realized that God had given him an unfair advantage over most living things. I guess he decided that he wouldn't shoot till he had to, and he had to today.
Obviously, Miss Maudie is able to recognize that Atticus doesn't value his gift of marksmanship the way the children would like him to. We can assume that Jem would have liked to know about Atticus's talent so he could brag to his friends about it. Readers know, though, that the most important thing to Atticus--and the lesson he would like his children to learn--is that being a good person who treats all others with respect and fairness is much more important than shooting a gun accurately.
Miss Maudie points out to Jem and Scout that Atticus is not particularly proud of his killing skill. After Atticus shoots the mad dog, Jem and Scout are surprised at both their father's ability with a rifle and his silence on the subject. Maudie gives them a lesson on humility. She tells them that although marksmanship is a skill that requires practice to achieve perfection, " '...shootin's different from playing the piano or the like.' " According to Maudie, Atticus felt his ability gave him an unfair advantage over animals, so he put down his guns for good. When Scout declares that he ought to be proud, Maudie retorts that " 'People in their right minds never take pride in their talents.' " Jem immediately understands Maudie's little lecture. He tells Scout to never mention it to their father because " 'Atticus is a gentleman, just like me.' "