Scout's Irrational Rationale. When Scout discovers the first gift in the secret knothole of the Radley oak, it turns out to be chewing gum. She restrains herself from getting "it into my mouth as quickly as possible," deciding to check it out more closely first. First she "sniffed" and "smelled" it; then
... I licked it and waited for a while. When I did not die, I crammed it into my mouth. (Chapter 4)
Atticus's Misunderstanding... Atticus is the one man in Maycomb people can count on to always do the right thing, to come up with the right answer. But he isn't thinking too clearly on Halloween night after Jem and Scout have been attacked. Although Boo Radley has carried Jem into the house, Atticus never considers him as the possible killer of Bob Ewell. Instead, Atticus believes that Jem knifed Bob, not Boo. Sheriff Tate tries to ease Atticus's mind, telling him that "Bob Ewell fell on his knife." Additionally, Atticus is slow to understand Tate's true intentions: Tate knows Jem is innocent, and that Boo killed Bob. Tate's version of the story gives Boo a way out of the public scrutiny he will encounter if he is charged with Bob's death. But Atticus believes that Tate is covering up to protect Jem, not Boo.
"I won't have it," Atticus said softly.
"God damn it, I'm not thinking of Jem!"
"... I do know that for once you haven't been able to put two and two together, and we've got to settle this tonight." (Chapter 31)
Maycomb's Usual Disease... Atticus begs the jury to look past Tom's black skin and the fact that Mayella is white. He knows he has little chance to alter the jury's perception about black and white, but he reminds them that it is an "evil assumption--that all Negroes lie, that all Negroes are immoral..." Nevertheless, the jury overlooks the facts and testimony, taking the white man's word over the black man's, and Scout later rationalizes their decision.
... in the secret courts of men's hearts Atticus had no case. Tom was a dead man the moment Mayella Ewell opened her mouth and screamed. (Chapter 25)