I've gotten horses here that have terrible habits- weaving, cribbing, and doing weird ritual motions. One horse would constantly turn around and bite herself. She'd walk in circles in a stall biting herself and would bloody up her sides. She was given to me as a lost cause. I turned her out in pasture and after she felt freedom, she never did it again.
I really do think that stalling horses is detrimental to their mental health. I understand some people have no other option, but its not an option I would take. I would LOVE to have a really nice barn with several stalls that I can use for quarantining new horses or for shutting up sick ones though.
Spent a whole hour today laying in a pasture, waiting for a sparkling vampire to show up. Alas, I woke up and looked over, only to find a mound of horse crap. Sigh.