If you are a C student, and your guidance counselor tells you to apply to MIT and Harvard, his advice may be delusive, or not based in fact, giving a false impression.
Your delusive hopes might tempt you to look away from reality, but if you believe delusive statements, you are deluded. What you believe in might be called a delusion. All of these words come from the Latin deludere which means "to play false, deceive." Also related to this word: Ludicrous. When you fall for a delusive idea, you are sometimes seen as ludicrous.