Why do you actually believe in God?

[robvalue]

Yes, reason can be unreliable, which is why we generate models and test them. That's science.

Of course, it's impossible to rule out the possibility that we're really in a mental institution and none of this is happening. But pragmatism is key. We learn, as best we can, about our environment. And we get good results. Whether or not any of it is actually "real" is only of philosophical importance. The models work within the environment.

If you wait for absolute certainty, you'll be waiting forever. People generally only retreat into this when they can't back up their own positions, and they try to drag everyone else down to their level.