Dressage Diva

DRESSAGE training or the horse, oh and in my case the rider.  Why is it that a person can intellectualize why and how, but when it comes to physical reality, struggle with the implementation?  After riding for many years, I am back to relaxing a minute muscle in my inner thigh that involuntarily tightens when I think a fearful thought on my horse's back.  Trying to be a Good Do Be, my horse slows down or halts.  I can feel myself thinking it.  But I can't seem to stop myself from thinking it. I can react,and push the horse on.  But in  order to prevent it?