Does society work out an unwritten, unspoken definition of the difference between faith and mental illness?

I mean, at some point, faith crosses a line and becomes a mental illness. There’s no written definition of this point but it definitely exists. Someone running and screaming along the street claiming that they’re being chased by a Nazi on a dinosaur is displaying the same amount of faith as someone claiming that a Jewish carpenter died for their sins yet one is potentially dangerously crazy the other is merely harmlessly crazy. How do we know this? Is it instinct?