Under ordinary circumstances, when you bring a newcharacter on stage for appearance in a novel or short story, you putter with your equivalent of a casting call, build an individual with traits and talents in some relationship to the story. Your first chore is to make sure there is some form of chemistry between that character and the protagonist.
Next step--you do a quick survey of individuals you've known in real life, whisk away some of that character's traits, shake the way a seasoned bartender shakes a cocktail, then you begin to write. As specific examples of this process at work, a former publisher for whom you worked and a former department head at a university you taught have turned into an aggregate of a quirky, self-involved sort of antagonist, someone the protagonist must suffer to some degree with each encounter.
Enter Angela Ayers, who came to life only two days ago as a means of bringing historical and attitudinal information on stage relative to a fictional town in New Mexico for your current project, The Robber Barons. When you began sketching a few notes for her, you realized she is entirelyfrom whole cloth. You don't know anyone from real life who in any way approximates her. You wish, in fact, that there were someone like her because you would immediately have a crush on her. That said, you put her to work. You were not surprised to discover, after you reviewed yesterday's pages, that your protagonist has a crush on her. He's not quite aware of the fact, but he surely will come to realize the chemistry of his attraction when he catches himself wondering if he can lure her from Albuquerque, where she runs a ladies' clothing emporium, to San Francisco, where her education, attitude, and intelligence could lead her to even greater levels of achievement.
The thing he doesn't know about her yet--but will soon discover--is that her father was not adverse to robbing the occasional train in Texas or the Arizona Territory. You only discovered this a few days ago. Given her polar-but-largely-admiring regard for her father, Angela also tried her hand at holding up a train, found herself enjoying the experience to the point where she did it again, and yet again. Thus she has become an invention of such singular importance that an outcome for her you'd not considered will have to be put into play. She has to go, which is to say she needs to be killed off. You have no idea how this will come about, but you have forty or fifty thousand words of text in which to make your discovery.
This represents the uncomfortable parallel between creating stories, with which you have some experience, and playing God, with which you have neither experience nor art. The closest you can approximate the former experience with the experiences of real life resides on the loves and losses you've experienced all these many years. You've lost grandparents, parents, friends, lovers, animals; you've lost a beloved sister and a beloved wife. One of the many reasons you're embarked on this book at all is to get a sense of a contemporary character, the 2020's, as it were, and his grandfather. You already know how your grandfather character is going to take the loss of Angela Ayers. You've been there, done that. Now, you get to write about it.