Why is it a mistake for an author to round out character who should remain flat?

A flat character is one who remains largely unchanged throughout a story. They may have one or two defining traits, but they do not grow or develop in any significant way over the course of the narrative. While this can be an effective way to create stock characters or easily identifiable archetypes, it can also be a mistake to round out a character who should remain flat.

There are a few reasons why it is important to keep a character flat. First, rounding out a flat character can make them seem inconsistent or incoherent. If a character who was previously stoic and unemotional suddenly starts showing deep feelings, it can feel jarring and unearned. Second, rounding out a flat character can take away from the overall impact of the story. If all of the characters are fully developed and sympathetic, it can be difficult for readers to focus on any one character in particular. Finally, rounding out a flat character can simply be unnecessary. If a character does not need to grow or change in order to serve their purpose in the story, then there is no reason to develop them further.

Of course, there are also cases when rounding out a flat character can be beneficial. If the character is central to the story, readers may need more depth and complexity to fully understand and connect with them. However, even in these cases it is important to balance the development of the character with the overall tone and structure of the story.