A secret is a useful thing for a protagonist to have or to find out. Your characters should possess not only agency—the ability to show initiative—but also an inner life. As you get to know them, you’ll learn what tensions they hold inside, and what contradictions, processes of reasoning, memories, frustrations, frame of reference, and pressures contribute to the force of individual personality. Your protagonist should be an underdog, disadvantaged by circumstances, vulnerable and apart from the crowd even as she is also caught up in the social swim of family, community, workplace, or other connections. As a rule of thumb, avoid letting your character be alone for too long to ruminate, stew, and philosophize.
However, brilliant exceptions come to mind. Consider “Tired Heart” by Keith Lee Morris. The narrator is hired by a shadowy stranger, a Mr. Griffith, to pick up mysterious packages during a cross-country drive, with the promise of big money if he delivers them on time. The narrator is alone for 3,000 miles, yet he finds himself twisted ever more tightly in an emotional vortex of fear, paranoia, and panic, because the directions keep changing, the destinations grow stranger, and he’s unable to reach his wife, though he calls and calls her. They’re supposed to rendezvous on the West Coast, but the narrator is dogged by setbacks, convinced he’s being followed and threatened. He loses his U-Haul and his truck and has to go on foot. When at last he finds his wife, she is sexually betraying him with his shadowy employer. Is the narrator dreaming? Insane? Lying? He’s real, he’s giving us his truth, and that’s what counts. And although he’s alone, the story is concerned chiefly with his human associations. Interaction with others is a key means of delineating an individual, and this narrator is desperately trying to make those connections. He doesn’t want this strange, secret life, but it holds him tight.
You can balance a character’s interiority against immediate, flesh and blood challenges offered by people in whom he has emotional investment, for good or ill. Troubled relationships and the secrets within them are the stuff of story.
Consider “Into Silence,” by Marlin Barton, about the strained relationship between a mother and her grown, deaf daughter, Janey. The controlling mother dominates the passive, resentful Janey and manipulates her by claiming to be sick. A stranger, Mr. Clark, comes to town and rents a room from them. Janey shows agency by going with Mr. Clark on photography excursions and arguing with her mother when they come home. By the end, Janey’s mother is dead, and Mr. Clark has left town. Having observed how the mother was stifling Janey’s spirit, he probably killed her. Janey herself can’t be certain how her mother died. The reader isn’t sure, either, but logic and intuition point to Mr. Clark.
My students were enthralled by this story and talked about it for over an hour. They debated explanations for the mother’s death and remarked on Janey’s odd relationship with Mr. Clark. Though it never becomes sexual, it has a romantic element. He behaves as a rescuer/destroyer, liberating her and leaving town without her. The price she must pay for freedom is keeping that terrible secret: matricide by proxy.
“Tired Heart” and “Into Silence” both deal with the distortion of an intimate relationship, the violent rupture of a bond as the result of the (suspected) actions of a powerful stranger and the protagonist’s exercise of free will. They’re examples I use when teaching and when musing about the kind of complexity I want my own characters to embody and to exhibit. The narrative has to spring from what’s inside—hidden, but generating exultation or despair.