The birth of an idea
I find that, most of the time, the best ideas are born from simplicity. Take for example, the hero or villain in a movie or book. Something truly painful happened to them. A really troubled past made them who they are, regardless of the powers, weapons, or toys for combat they use now. Focus on the psychological change of each one of them.
And that is simplicity, because we have all suffered; so we can all relate to suffering and the psychological changes one may experience. All we have to do is take the suffering and add some interesting and creative experiences that shape the mind accordingly, and then we have a new character.
Driven characters
I make the character go through self-doubt, self-pity, anger, and all kinds of simple but real feelings. After all, my feelings lead me through my life, and they also lead the characters in my stories in order to be real like me. All pain and suffering exists in my life for a purpose, whether I like to admit it or not–school bullying, surgeries, separations, loss, bigotry, etc.
That exists to make me stronger. In the same sense then, a fiction character must allow himself to feel all his pain and go through a challenging transformation process; and then decide if to follow his anger as the villain, or to learn from the pain and gain strength as the hero.
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