However, as the author, you must know their backstory. Otherwise, you won't know how and why your characters react as they must under pressure. Loyalty vs. Greed. Honor vs. Cowardice. Love vs. Fear.
True characters struggle with internal choice.
In commercial fiction, heroes and heroines will make the right choice, no matter the personal sacrifice. Villains choose the wrong path and pay the price during plot reversal at the denouement. Armed with the character's background and personality, you are ready to begin the story which should launch in full stride with an immediate change threatening the character's well being. You see your characters clearly. You've created them.