Two minor points:
1) What is truth? How do you know whether something is true? By perceiving it? Is your perception not influenced by belief?
I'm not saying that we cannot know truth, ever. But we have to keep in mind we might be wrong, too...
2) Believing in something might _make_ it become true. Or, to put it differently: Belief may lead to actions which change reality - essentially a self-fulfilling prophecy.