At the risk of sounding VERY VERY OBVIOUS I think the hardest part of character-driven writing is writing about human beings instead of ideas. So often I’ll be crafting something and realize, I’m thinking about an idea, not an actual person. People aren’t paragraphs, you can’t predict them or plot them out or put them on notecards tho you might be asked to. You have to find a way to turn off the part of you brain that’s floating above the story, writing an article about the story, you have to stay inside of it, at the table with the character and just watch her eat butter off the end of her knife, you have to be quiet enough to sit with her and insightful enough to know that really it’s more than the butter, and the knife, and if you end up with ALSO a brilliant idea, then it must be an accident, a coincidence at best, it can’t have been the plan all along.