It's like if Eeyore had a little brother that was only allowed to leave the attic on his birthday.
We're serious right now: It's damn near impossible to find a picture where they don't look depressed or tired from mocking natural selection with every second of their existence. The mini horses are literally dwarfs, created by the passing of the equine dwarfism gene. Perhaps the plan was to breed a proportioned, smaller version of a regular horse (for which we would pay 20 buttloads of dollars), but instead the animals ended up with grossly enlarged heads and a dark wonderland of health problems, including complicated births and leg deformities.
Mini dwarf horses have been known as a particularly "calm" breed, although we think people are confusing calmness with the horses' constant, paralyzing fear that they'll be attacked and eaten by an elderly, arthritic coyote.