IT depends on the horse. Some I feel instantly at ease no matter how they behave, I just have this feeling that they won't do anything intentianal to hurt you. One example was this basically unbroke Morgan gelding I rode for a friend of my moms. Beautiful horse, but had the worst ground manners and his behavior under saddle wasn't much better. He was extremely disrespectful, but I never felt scared of him. Wary, knew I had to stay on my toes, but never actually scared.

Faith I was initially uneasy about...never got to scared, but definately didn't feel comfortable. However after 4 years of owning her I am now very comfortable and have gotten to the point that I do trust her, but she will probably never be a horse I would let anyone ride. She wouldnt' do anything to someone, just gets really pissy if her rider doesn't have careful hands and seat and is rather over reactive so you have to be subtle.

I have had several horses that I have been very nervous about, really for no reason. Just this gut feeling where I really wanted nothing to do with them. Some of them have later proven to be untrustworthy, other haven't, but I never kept them around long enough to really find out, and definately never bought one and tried to work through it, to many horses that I don't feel that way about to try and find out why