One of the issues some horses have with being
ponied for the first time, is to have a rider up "above" them, asking them to
lead. They are used to us on the ground, but get above them while mounted on the
other horse, and I think that it is partially that flight instinct of something
above them. I have worked on some by having them held or tied at a strong fence
that I could climb up above them, and then get a hold of the rope, and ask them
to come forward, and even give them a treat if needed. Just not a natural
position for them to walk forward towards something up above them like that.