In Chapter 6 of To Kill a Mockingbird, Scout senses that changes are taking place in Jem. After they are caught sneaking around the Radley house and Jem's pants catch on a fence after he attempts to peer into a window, and Mr. Radley's shadow appears, then fires off a shotgun. Of course, Jem has had to climb out of his pants; when the children are caught in their mischief by Atticus, who comes out after the gun blast, Dill lies, telling the adults that they were playing strip poker. Jem mitigates this lie by saying that they were playing with matches, instead. At this point, Scout declares,
I admired my brother. Matches were dangerous, but cards were fatal.
However, later, in his maturation, Jem becomes brave enough to retrieve his pants from the fence at the Radley house where earlier he tried peeking in the window. Before he goes, he tells Scout that he does not want to get into trouble with Atticus, and if he leaves his shorts on the fence, he certainly will.
Maybe so, but--I just wanta keep it that way, Scout. We shouldn'a done that tonight, Scout.
It is then that Scout declares that they first began to part. She has had moments of incomprehensibility of Jem, but this is a major moment, for she does not understand his guilt and his acknowledgement of the attitude of Atticus, that they should be respectful of the Radley's desire for privacy.