What is the main lesson that you learn from The story of Tam and Cam?

Easily drawn through the conflicts in the story, Tam's life is: Good always triumphs over evil, and Tam's incarnation is the expression of vitality, the fierce rise of man in the face of evil. stamping of evil. But through that we also learn other lessons such as No one is perfect or all-round good and no one is bad for everyone.
Firstly, we think that Tam is a good, gentle person. But why do good people take revenge that is both poisonous and profound (According to the original, Tam not only poured boiling water to kill Cam but also made fish sauce and brought it to his stepmother)?
Second, we also often assume that stepmothers seem to be all bad people. But in fact, they are just not good to other people, but very good to their own children. The stepmother did everything just to think about Cam.