Editors and agents frequently state they are looking for fully developed characters (among other qualities) in their incoming manuscript submissions. I will dissect a fully developed character into three parts.
First, the outside veneer: education, job, income, family groups, friendships, religion, political persuasion, social status, what car do they drive or sports do they play, etc.?
Second, we move to the insides. Does your main character have a warm, gooey center or a cold, callous heart? How do they feel about the other characters in your story? What do they think of them? Whom do they hate? Whom do they love? What are their wants, needs, desires?
Third, consequences, and my favorite one. In your stories, as in real life, there are consequences to one’s decisions and if your characters are to be authentic, sometimes that means the characters get the stuffing kicked out of them.
In THE CHOCOLATE WAR by Robert Cormier, Jerry Renault, a high school student refuses to sell chocolates in the mandatory school fund raiser. Every day, when the teacher asks how many chocolates he sold, he says none. At first, he is hailed as a hero, but quickly becomes a threat to the school gang, the Vigils, and the school administration. His defiance pits him against everyone and it won’t be solved without bloodshed. If the author had written a different ending (everyone shakes hands and all is forgiven), it would not feel nor would it be authentic.
In WONDER by R.J. Palacio, Auggie, a fifth grader, born with a facial deformity is also the new kid at school who wants to be like everybody else. But he is constantly teased, stared at or ignored. Auggie is a brave boy who handles the constant cruelty with humor and self-deprecation. The reader falls in love with Auggie and wants him to spend time with friends and not be tormented. But that’s not real life. When he’s in the company of strangers, something will be said or someone will stare. It would not be authentic if the author wrote those scenes differently.
It can be painful to write those emotional scenes, but if your story is to be authentic, the writer must do it.