Dwarves get psychotic when they see the sky. They have some weird dwarven word for "sky madness," that they call it, because I haven't decided whether I'm going to go for "old and germanic" for dwarven, or "lots of 'kh' and 'g' and 'd' and little triangle things over the vowels." Everyone else mostly just assumes that dwarves are all nuts, especially in the Southern Lands, where it's more common.
It's really the night sky that's a problem, the stars or the planets or the moons. And for most dwarves, it's not really a huge problem. In ages past, a dwarven sorcerer-king learned to craft a sort of charm that mostly protects against the curse, or whatever it is, and with these forged the first above-ground dwarven empire. Nowadays, like most of dwarven government, they're largely religious in character, and the priesthood controls their manufacture.
It still comes up often enough that that's what a lot of people think of when they think of dwarves: weird, psychotic, atheistic serial-killers. Usually it happens to dwarves who have been exiled, but every so often, for whatever reason, the charms don't quite work.
And that's why dwarves are crazy.