Atticus Finch, the father of Jem and Scout, is an extremely talented and intelligent man. He takes each of his roles (father, lawyer, neighbor, citizen, friend, etc.) seriously and does his best to make the most of each. Atticus attempts to address each situation in which he finds himself in the best way possible according to his morals and ethics; two of his most memorable and telling traits are fairness and humility.
In Chapter 10 of To Kill a Mockingbird, Jem and Scout are shocked to learn that their father is an exceptional marksman. Prior to his having to kill Tim Johnson, a rabid dog, Atticus had revealed his skill to his children. Although the children are excited by their father's prowess and subsequent nickname, "Ol' One-Shot," Miss Maudie Atkinson explains that their Atticus has his own reasons for not bragging about or flaunting his ability.
"Wonder why he never goes huntin' now," I said.
"Maybe I can tell you," said Miss Maudie. "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 have given him an unfair advantage over most living things. I guess he decided he wouldn't shoot till he had to, and he had to today...People in their right minds never take pride in their talents..."
Atticus's senses of fairness and humility simply would not allow him to misuse his skill as a marksman.