on Jane Friedman site:

I write a lot about character arc, and I talk a lot about it with my clients.

Because if there’s a magic bullet for creating a novel that sucks the reader in, holds her attention, and ultimately makes her feel like it was worth the 6+ hours it took to read that book, character arc is it.

Many writers are clueless about the importance of a character arc for their protagonist, but I find that even those who do understand how important it is often still don’t know what it takes to actually make one work in practice.

Basically, there’s one key mistake they’re making: When it comes to the major events of the plot, they’re focusing on how their protagonist feels in the moment, based on different issues in their past, rather than on how that emotional reaction connects with their character arc.

To show you how this works in practice, let’s build a little story, starting with just the plot.