You are not really believing then, you are pretending that you believe you will not fail. Keep in mind that even though a positive mindset does help, it is not crucial to have lucids. The first time i tried lucid dreaming, i was skeptical on the concept to say the least. But once i had my first lucid, that all changed and I started having them a few times a week. Just know that ALL people can lucid dream and if you keep at it, its almost guaranteed you will succeed. :p