Why does Scout cry after returning home from the jail in chapter 16?
Scout is such a sweet, innocent, and naive little girl. She ran into the middle of a lynch mob because she heard her father say, "Do you really think so?" (152). She thought that somebody was going to "get jumped" and she ran in there to watch. On the way home that night, however, Scout realizes that maybe what she had done was dangerous. Had she known the real reason the men were at the jail, and the real reason why her father was there as well, she may have not acted so hastily. It's a good thing that Scout did run into the crowd because she ended up changing Mr. Cunningham's mind about lynching Tom Robinson and he called the mob off. Scout realizes the possible danger she ran into that night once she gets home:
"We had come in quietly, so as not to wake aunty. Atticus killed the engine in the driveway and coasted to the carhouse; we went in the back door and to our rooms without a word. I was very tired, and was drifting into sleep when the memory of Atticus calmly folding his newspaper and pushing back his hat became Atticus standing in the middle of an empty waiting street, pushing up his glasses. The full meaning of the night's events hit me and I began crying. Jem was awfully nice about it: for once he didn't remind me that people nearly nine years old didn't do things like that" (156).
Many times people rush into situations without fully analyzing the possible consequences. This is a great experience for Scout to learn to look before she leaps next time. Nevertheless, it turned out well enough in the end.
Atticus is staying at the jail to protect Tom Robinson. When Jem and Scout go to the jail, Scout is the one that breaks up the mob that was there. Her innocence and friendliness makes the men go away. She isn't aware at the time, of what the men were about to do. Only when she returns home, does the reality of the whole thing, hit Scout. She breaks down and cries about the ugliness that she had just been witnessed to.
In all of her innocence, Scout looks at life with the childlike eyes she has. In that one instance, Scout is thrown into the reality of how the world works. She sees that the men could have easily have killed her father, and if given the chance, they would have killed Tom. Scout sees first hand the ugliness that is a part of her town. She is aware that there are some people that are just plain nasty. In her short life, Atticus has protected his children from the hatred he has to deal with, but by taking this case, he knows that the ugliness is sure to come to them.
Scout's world was changed that night. She no longer had the innocence of childhood, she now had the harsh reality of what hatred and ignorance could bring.
Scout cries because, as she notes, "the full meaning of the night's events" strike her. To be specific, she realizes that people wanted to kill her father, and, more generally, that people hate so intensely and so blindly that it seems that other people aren't human to them.