If you read William Golding's The Lord of the Flies, you will see that the theme of good vs. evil in human nature is a huge part. I think it's also probably present in the Hunger Games series.
The witches show the fact that if you turn bad you will be punished, this is shown by Macbeth who was first seen as a hero who then turned bad dreaming of becoming king and got caught up in greed...
The Hobbit, by J.R.R. Tolkein, has many themes in it, these include adventure, wealth, greed, good and evil. Tolkien shows the battle between good and evil, through the different characterizations...
Under every evil is good and under every good is evil.so if your little sister acts unusually nice to you then she might have a bad reason under that and vice versa.