I think the best piece of character design advice I ever received was actually from a band leadership camp I attended in june of 2017.
the speaker there gave lots of advice for leaders—obviously, it was a leadership camp—but his saying about personality flaws struck me as useful for writers too.
he said to us all “your curses are your blessings and your blessings are your curses” and went on to explain how because he was such a great speaker, it made him a terrible listener. he could give speeches for hours on end and inspire thousands of people, but as soon as someone wanted to talk to him one on one or vent to him, he struggled with it.
he had us write down our greatest weakness and relate it to our biggest strength (mine being that I am far too emotional, but I’m gentle with others because I can understand their emotions), and the whole time people are sharing theirs, my mind was running wild with all my characters and their flaws.
previously, I had added flaws as an after thought, as in “this character seems too perfect. how can I make them not-like-that?” but that’s not how people or personalities work. for every human alive, their flaws and their strengths are directly related to each other. you can’t have one without the other.
is your character strong-willed? that can easily turn into stubbornness. is your character compassionate? maybe they give too many chances. are they loyal? then they’ll destroy the world for the people they love.
it works the other way around too: maybe your villain only hates the protagonist’s people because they love their own and just have a twisted sense of how to protect them. maybe your antagonist is arrogant, but they’ll be confident in everything they do.
tl;dr “your curses are your blessings, and your blessings are your curses” there is no such thing as a character flaw, just a strength that has been stretched too far.
