After Uncle Jack spanked Scout without having heard the full facts of her fight with Cousin Francis, he returned to Scout so that he could finally hear her side of the story. Scout boldly told him that
"... you ain't fair.
"I reckon I love you even after what you did, but you don't understand children much."
After hearing the whole story, Jack was ready to return to Finch's Landing and tell Alexandra what Francis had said about Atticus. But Scout made him promise to let it go and not tell Atticus about the real reason (that Francis called them both a "nigger-lover"). When Jack later spoke with his brother, he told him that
"I shall never marry, Atticus...
"I might have children."
Atticus said, "You've a lot to learn, Jack."
Jack learned the hard way from Scout to always hear both sides of the story, and that children don't always tell the truth. He learns from Atticus to always answer a child honestly and forthrightly, instead of veering off in other directions, as he did with the story about Lord Melbourne after Scout asked him "What's a whore-lady?"
"Jack! When a child asks you something, answer him, for goodness' sake... Children... can spot an evasion quicker than adults, and evasion simply muddles 'em... you had the right answer this afternoon, but the wrong reasons.