Advice on writing fictional characters which I find helpful:
“Often as not, when I have a character who’s not clicking, it’s because I haven’t found what they’re angry about yet.
My favorite fictional characters are the ones who cannot witness evil being done without becoming fired up about it, and I have all the time in the world for characters who will go to the ends of the Earth to right a wrong. But I also have boundless love for characters who hold petty grudges, who are still stewing about something that happened to them in seventh grade, or who are just grumpy cusses. A character who is supposed to save the world, but can’t let go of an incredibly minor vendetta, is automatically fascinating. And utterly believable. That’s the great thing about anger, after all: it doesn’t really come with a sense of proportion.”
—Charlie Jane Anders, Never Say You Can’t Survive: How to Get Through Hard Times by Making Up Stories, Tordotcom (2021), Chapter 12.