From THTF P. 300: Chapter 9, "Meanings"

BAD HORSE: It’s a good subject to talk about, but you have to figure out what made that horse the way he is. Was it the way that horse was handled or was it self-preservation that made him do things that weren’t good for him, or good for the human either? He’s really just a confused horse so we wouldn’t use that word “bad.” There aren’t any bad horses, they are just mixed up and it’s important to know the difference. Because the horse had the wrong feel presented to him, the person and the horse both missed that right way to feel of each other on the start. This sometimes leads to people using this word about a horse, but it could sure be forgotten about if certain things shaped up.