Originally Posted by mirr0rz
I don't understand that. How can you not know if you believe or not? Either you believe in God or you don't; I don't see how there's a middle ground.
Here's a better explanation of it.
The theist will say, without a doubt in his mind, that "yes, indeed God does exist."
The atheist will say, "no way in hell that a God exists, it's just not possible!"
The agnostic will say, "I don't have the evidence to either confirm or deny the existence of God." or something similar.