Dwarves cannot endure loneliness and become erratic and obsessive when exposed to solitude; this is normally addressed by making sure dwarves need not be alone.
Elves easily suffer from delusions or paranoia. They often feel like they're missing out on some greater truth they could understand if only they opened up towards... something. It can be difficult to keep track of the longlived elves and their issues to get them help in time. These are but two examples; all species have their peculiarities.
"At first it looked like a simple poisoning, nothing to worry about. Then she started seeing things and talked to the forest. On the fourth day, she bit Relgaan and fled into the canyon; Relgaan has never spoken again."Time and again, people leaving the Area think themselves to be the servants of Starmaker, and of course her favourite. These raving lunatics pursue unfathomable goals, sometimes even violently, and almost always end up in the voices' care.
— Orewasse, traveller
Goldfairies are hard to understand at the best of times. They all have secret goals and one together, it seems; they can often be found talking to themselves or the furniture, and stop in midsentence when they become aware of company. It requires patience to handle them.
"Sanity is a matter of circumstances. Are the Redforesters insane for living in poison? Is it mad to build on a volcano?"
— Hafana, scholar
There are plenty of dangers - wild animals, illnesses, curses, volcanoes, elementarians... but I didn't want to leave out insanity. After all, it's a good explanation for some rulers' behaviour. And I like it better than them being eeeeviiiil; since I ruled out the Evil from Genius Loci, I thought it'd be better to blame it on loss of mind when rulers become cruel.