Other forms: paralogisms
A paralogism is an unintentionally misleading argument. Even if your friend has convinced himself it's true, you'll still be frustrated by his paralogism, "I never wash my hands because germs are actually good for you!"
The Greek root of paralogism is paralogismos, "reason falsely," and it's where people end up when they base a belief or statement on false reasoning. It's mainly used in rhetoric and philosophy for a fallacy the speaker believes is true, rather than one deliberately meant to deceive someone. It's a paralogism to conclude that because your plane flight went smoothly when you wore your lucky socks, you won't be safe on airplanes without them.