This is just an example of getting a start on overcoming fear. Is Lucky over his fear completely forever...? No - I continued to work with him for the next couple of weeks each day after his training session and he continues to overcome more of his fear and build confidence. When he goes home with his owner, his owner will continue to build on this foundation as well until one day - he will be over his fear completely.
The fly spray may represent anything that they are fearful of - water, tarps, plastic bags, etc. Everytime I work with a fearful horse, I go over in my head my 3 rules, #1 - I cannot get hurt, #2 - The horse cannot get hurt and #3 - The horse must be calmer at the end of the training session than at the beginning.
With these 3 rules in mind, a confident and calm demeanor and patience - you will be the partner your horse deserves.