In a post on Writers in the Storm, Shirley Jump says that creating impossible choices can force your protagonist to overcome their internal obstacles, whether they want to or not. “Impossible Choices are fantastic for raising the conflict and tension in your book because the reader is dying to know how it works out,” she says.
A high-stakes example of an impossible choice is the one presented to Sophie in Sophie’s Choice. Set during the Holocaust, Sophie must choose which of her two children will stay with her and which will be sent to the gas chamber.
Your protagonist’s choice may not be as gut-wrenching as that, but your characters don’t have to know that. They only have to feel the stakes are that high. To accomplish that, Jumps says that your hero’s external goal, motivation, and conflict should be in direct opposition to the internal goal, motivation, and conflict. Jump provides an example using Richard Gere’s character in Pretty Woman.
Jump recommends analyzing what you read and watch to find these impossible choices. List the internal and external goal, motivation, and conflict, and assess how they impact the plot, engage you as a reader, and affect the overall story.