You can think of "believe" and "believe in" as two different things. "believe in" is a phrasal verb. Often in English, a verb (such as "believe") is combined with a preposition (such as "in"), or an adverb, or both, to create a new verb that can have a different meaning. See http://en.wikipedia.org/wiki/Phrasal_verb "believe" means you think someone is telling you the truth. He said Tokyo is the capital of Japan, and I believe him. If I keep telling myself that she loved me, maybe one day I will believe myself. (Maybe one day I will finally think that is true; right now I know I am not telling the truth. :-) ) "believe" can also mean you think something is true - that it, that you have a certain opinion I believe it will rain. (You think it will rain.) "believe in" can mean you think something is real and exists: I believe in God. (You think God exists) I don't believe in ghosts. (You think ghosts do not exist.) It can also mean as azimux said, to have faith or trust in someone or something, and think they will succeed: She will be a great actress one day, I believe in her. If I keep practicing, I will run a mile in less than 4 minutes. I believe in myself. "believe in" can also mean you have a strong opinion or conviction: I believe in exercising once a day. (You think it is important to exercise every day.) I believe in saving money. (You think it is important to save your money instead of spending it).

no need to believe in yourself, just believe in me :P