Raymond Chandler knew what he was talking about when he said, “When in doubt have a man come through a door with a gun in his hand.” The man with the gun might be anything—a postman with an important letter, a phone call asking the protagonist to contact her lawyer immediately, or, as here, an aspect of the protagonist’s own character; the essential thing is that you, the storyteller, didn’t know about it in advance. You didn’t plan it. It takes you by surprise, and opens up new possibilities, and forces you to come up with solutions you wouldn’t have had to think of otherwise.