“And secrets are dangerous. They start small but grow with every evasive answer or outright lie that protects them. Nevertheless, I confess to finding the closeness such conspiracy breeds irresistibly delicious.”

― Paula Brackston, The Witch’s Daughter

Pinocchio, as I’m sure you know, had a nose that grew with every lie he told. Well, now you’re going to create a character very similar. Your character cannot tell a lie without it coming true. Obviously, it never works in his favor. For example, if his lie was “I have a girlfriend,” he would not suddenly have a beautiful, brilliant woman hanging off his arm, but rather a hideous ogre or, maybe, just a nihilist. After a few good lies, he was starting to learn his lesson, until his mom asked him a question he just couldn’t answer, and his world started crumbling around him ever since.