Some blogs, usually the controversial ones, take longer to come to the boil than others while I think whether I should say anything.
There are very few people who can cope with a sharp horse, either on the ground or when ridden, so why would you want to make a horse sharp? Responsive yes, sharp no. Responsive requires the horse to think and then react appropriately in a way that he has been taught whereas sharp just means that the horse reacts like a horse, like a prey animal - flight first and maybe think later.
Horses become sharp when they are confused about what they are being asked to do or frightened of the consequences of not doing anything. Take for example the practice of insisting that a horse always faces you - this is very common in many so-called natural horsemanship training systems. Unlike IH, where standing quietly with the handler is always reserved as a comfortable place, these systems use an alien cue such as rope swinging to make the horse move and turn. If the horse doesn't understand the cue then the end of the rope (which stings) is used first to touch the skin, then the muscle and then the bone, to hit the horse until he works out that he needs to move away. Often it takes the horse a long time to work this out, especially as he has a natural automatic, instinctive, non-thinking into-pressure reaction which means he absorbs the pressure and the pain because his body wants to move into it. Once he does get it - usually after he has offered all sorts of other behaviours in his repertoire - he learns to move away and move away quick.
Why would you want this other than to dominate? Why would you want a horse to always face you anyway? Some horses will go through and out of the other side of this training and learn to face without much angst, more with resignation. Others just become sharp and worried.
Add all of this to a horse that is already naturally sharp and it can be a dangerous combination - leading to behaviour like bolting. In Jessica's case, where she has had a little of this type of training in the past, it means that if you get at the wrong angle to her she panics and canters around you with her back legs so that she can get out of the way of the anticipated sting. Fortunately we have found an off button which is just a flat hand pushing against her haunch which once again activates a natural (and this time very much wanted) into-pressure response and gets her to stand still and come back down to earth. As a result she now stands still for tacking up and to be mounted. She's also more willing and able to give things a go now and you can see the cogs going round as she works out how to tackle something new. IH created the peacefulness and clicker created the imagination.