I'm back to working on my novel, and the characters for that story. This round of development is their flaws. And it's important for me to get right because it determines not just the character arc, but the story itself.
Also, the protagonist's flaw dictates all of the other characters' flaws because the other characters will be viewpoints on the protag flaw and reveal different worldviews on it.
So the flaw covers how a character might heal from two possible angles: serving others or seeing the self honestly. This can be in any combination or order. The protag might have to see the self first clearly to help others, or might have to help others before she can see herself. Or the story might just be all about internal reflections or just all about external actions. Then again, the protag might not quite learn anything at all. But I think that's advanced writing techniques not meant for us mere mortals...
The protagonist has a need that she doesn't know about but needs to fulfill. The flaw blocks that need. Over the course of the story, the protagonist's actions and decisions will either strengthen the flaw and/or make it more dominant or weaken the flaw and/or make it less dominant. Near the end of the story the protagonist demonstrates that she has overwhelmed the flaw and conquered it or has been overwhelmed by the flaw and been consumed by it.
The flaw may be hidden to the protagonist at first because her life has allowed her to work around her flaw, or at least live with the flaw unchallenged. She might even see her flaw as a strength. However, the impending story comes along and shows her flaw for what it is--a weakness. It holds her back, forcing her to try new strategies and learn different methods/ways of thinking for dealing with problems. She can no longer strive for what she wants with the flaw in her life as it is. Something's got to give.
Will it be her?