Jem and Scout complain about many things to Atticus throughout the novel. For example, they complain that Atticus is too old, that he can't do anything that other fathers do such as play football, and that he has a boring job. Scout also complains about school and the growing pains that come with the school experience, while Jem complains about having to read to Miss Dubose after ruining her flower beds.
Atticus' main response to his children in any of these situations is always one of learning. For example in response to Scout's complaints about school and trying to understand her teacher, Miss Caroline Fisher, her classmates, Walter Cunningham and Burris Ewell, Atticus tells her in chapter 3,
“First of all,” he said, “if you can learn a simple trick, Scout, you’ll get along a lot better with all kinds of folks. You never really understand a person until you consider things from his point of view—“
“—until you climb into his skin and walk around in it.”
Similarly, Atticus uses this same concept with Jem in regard to Mrs. Dubose. Thus, as part of Jem's growing experience he learns that it must have been painfully difficult for Mrs. Dubose to refuse her morphine and die a painful death.
In another lesson, Atticus defines true courage as knowing you are defeated before you begin, but seeing it through to the end anyway. Jem applies this lesson to both Mrs. Dubose and his lack of understanding to Atticus' persistence in defending Tom Robinson.