What truly motivates your character? I'm not looking for the easy answer here. I want you to dig down deep into their psyche and figure out what is really motivating them. Take my new main character for example. It's easy to say she wants to avenge the death of her brother. But that is what she wants, it isn't what motivates her. What motivates her is the tremendous hole eating it's way through her soul because he died fighting on the battlefield and she wasn't there to help him. What motivates her is that he was the only one in her family that saw her for who she was and supported her dreams.
To figure out what their motivators are look to their past. Is there something about the way they were raised that may affect their motivations? Is there a relationship that may be a driving force for them? Family, loved ones, or lack thereof all affect your character. What are their beliefs, culture, customs, occupation? All of those factors affect motivation and the way a person deals with life.
After you've figured out your character's motivations you must figure out what they want, which should be easier to do now that you've dug deep. My main character doesn't want to kill the man who killed her brother. What she truly wants is to feel supported and loved and to know that her brother didn't die in vain. Will she get that? We shall see. Do you know what your characters' motivations and desires are?
For more advice on characters check out this great post from Writer's Digest on How To Up The Ante For Your Character.