Atticus Finch is an example of a truly good man, who seems to always do his best to see the good in the world and to refrain from juding others harshly. While Atticus does not condone inappropriate actions and reactions in anyone, he does view others and their deed with consideration and compassion. He does not excuse those who are guilty of wrong doing, but does attempt to make sense of their mistakes and understand that errors are often made out of ignorance, rather than malice. These traits are made evident on page 30 of Chapter 3 (of my copy), during Atticus's discussion with Scout, which takes place following Miss Caroline's first day of school and subsequent run-in with Burris Ewell and misunderstanding of the Cunningham family, as well as Scout's own difficulties.
Atticus said I had learned many things today, and Miss Caroline had learned several things herself. She had learned not to hand something to a Cunningham, for one thing, but if Walter and I had put ourselves in her shoes we'd have seen it was an honest mistake on her part. We could not expect her to learn all Maycomb's ways in one day, and we could not hold her responsible when she knew no better.
This indirect quote reveals Atticus's understanding of the harm often caused by ignorance. He was aware that Miss Caroline had been wrong in her actions, but also that she had meant to be a help, rather than a hindrance. This trait of Atticus's is repeated throughout the book, but is emphasized most in his undertaking of Tom Robinson's defence during his trial.