Are there any intances in To Kill a Mockingbird where life lessons were learned because wise decisons were made?
I think there are many instances of this in the novel, but one big one that I can think of is the decision not to go ahead and arrest Boo Radley for killing Bob Ewell at the end of the novel when Boo intercedes and saves Jem and Scout from being hurt or killed by the slimy piece of white trash. This is a hard decision for Atticus to make, because he is a lawyer and he is sworn to uphold the law, not circumvent it. He is conflicted over doing the right thing, which is not to turn Boo in and the wrong thing, turn him in. He knows that if he were to obey "the letter of the law" then he should tell the truth, but instead, he doesn't lie, but he remains neutral, which sometimes is just a sugar-coated lie. Atticus knows this. He is a character with impeccable integrity, that's what makes it so hard. In the end, though, he makes the difficult decision of choosing the well-being of the man, Boo, over the strict interpretation of the law. Sometimes we must answer to a higher power.
In the beginning of the novel, Scout and Jem are told that it is OK to practice their shooting on annoying birds like crows and other nuisances, but they never should kill a mockingbird because all these birds do is sing all day and make people happy. They are innocent and fragile little birds. When Atticus explains to Scout why he has decided NOT to turn Boo in, he asks her if she understands and she replies, yes, that it would be like shooting a mockingbird. She has learned the lesson from Atticus' hard decision.
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Other examples of lessons learned when wise decisions are made in To Kill a Mockingbird:
MRS. DUBOSE. Atticus forces Jem to read to Mrs. Dubose after he destroys her camellias. Jem learns that an uncontrolled temper and vandalism has its repercussions; he also learns from Atticus about a different kind of courage.
SCOUT RETURNS TO SCHOOL. Scout wants to quit school after her bad first day with Miss Caroline, but Atticus convinces her to return. Although school is only minimally better for her, we know from the grown-up Scout that she prospered later in life after returning (and becoming a writer?).
JEM'S LOST PANTS. Jem returns to the Radley's barbed wire fence to retrieve his lost pants because he does not want to prompt Atticus' anger or lack of trust. Although this seems a bit deceptive on Jem's part, he later explains it to Atticus, who is sympathetic to Jem's actions.