Believing it to be true does not make it true, in and of itself. I believe in the things I've seen, because I have seen them for myself. That's a personal and subjective thing, though. I cannot expect others to believe them outright, because they have not experienced them.Could you elaborate a bit on how you can believe in something while not believing in it? That's honestly not meant to be a flippant question.
To be put it another way, I'm just not an absolutist when it comes to my beliefs. I'm a relativist. I know that beliefs are not objective; they're opinions. I don't think others are wrong just for not holding the same opinion as me. That would be really arrogant and juvenile.