Why might an author choose to use the 'evil twin' trope?

Using the 'evil twin' trope provides an author with a powerful tool to delve into profound themes of identity and morality. This narrative device allows the exploration of the duality of human nature, where characters can embody contrasting traits or ethical dilemmas. Through the relationship between the good and evil aspects represented by twins, the author can challenge readers to reflect on concepts such as good versus evil and the complexities of personal choice. Additionally, this trope can provoke questions about whether one's environment or personal decisions define their moral compass. The exploration of these themes can create a rich and engaging story that resonates on multiple levels with the audience.