Headstall

For over a year, I have easily put either a bridle with a snaffle bit or a hackamore on Zum’s head. Suddenly, Zum wants no part of a headstall anywhere near his head. So I am back to putting ropes around his ears to help him accept things on his head. I do not understand his sudden rejection of things he knows. Is he testing me? Is he just acting like a young and inexperienced colt? Or is this part of the learning process? Two steps forward and three steps backwards….