For me, adding details to characters has to be one of the hardest parts of writing. Their history and appearance come easily to me but things like speech patterns, conscious choice making, level of intellect and their personality kind of get hard for me to establish and maintain.
Without knowing these kinds of things, character development gets tricky. Any decisions made by certain characters won’t seem realistic after certain events occur.
I guess this means I need to take a few weeks out of my writing schedule to learn more. The path a writer takes is one that requires you to learn and improve.