I recently had an interesting experience. I watched a horse get trained for the period of three months. This horse hated being touched in the rein and was difficult that way. After some experimentation the horse prefered a nickel free bit. This helped somewhat but she still had a significant problem when asked to bend while traveling to the right.
The rider after switching bits just decided not to touch her and keep her happy. But the correct way to engage a horse is to have the energy come from behind and then guide the energy with the reins. This helps the horse relax and build top line and flexibility. When the rider was asked one day to ride the horse forward into the bridle the horse acted stressed out and refused to go and bend. When this happens it is time to check the teeth for a possible floating issue. The horse was floated and she had three year old molars that were in the process of coming off. She had scrapes inside her mouth from this. If the rider would have ridden the horse forward into a little contact, this problem could have been identified and solved right away and the horse would not had to have had so much discomfort.
If you are riding your horse correctly and you encounter a problem. Please take note and look for a physical problem. The worst thing you can do is pacify the horse and possibly cause more discomfort accidentally.