Or maybe you know what you believe. You just aren't sure if it's the truth, right?
Anybody saying that they know the truth is a loony. Sure fire faith is just stupid. Nobody knows the truth. Nobody knows what keeps the universe together. Science hasn't even begun to have a comprehensive model for how it works. It's at best qualified guesswork.
The religious debate is whether or not people think that people having epiphanies in deserts had a more accurate scientific model than cutting edge science today. I personally think that's highly unlikely.
Christians saying they "know" that they'll go to heaven are just plain deluded. None of us knows. It's all about which horse we're betting on.
I'm betting on that we're all wrong. Time and time again science have shown that the true theory was one that earlier had very few supporters. Aristotelian physics was the "bible" of all science for 2000 years and today we find all his theories laughable.