Jesus was just a liar. You know, during those 18 years that he wasn't present, he was in Tibet, learning with the monks. Then, when he came back, he wanted to bring all this spirituality to his people, but they wouldn't get it, so he added all their religion to it and gave himself some credibility by saying that he was the son of god.

You can find more proof of this travel of his in the Apocrypha.