Over the two and a half years that I've owned him, there have been a few times where we've had some pretty big fights, the snaffle bit issue comes to mind. His first owner warned me: when he doesn't like something, he's very vocal about it. She experienced his attitude when she tried to use a saddle that he didn't think fit him well. I now know that if he is really resisting something, he's probably physically uncomfortable.
Over the past year or so, getting Izzy to stretch his topline and neck has been a problem. He's a pretty insecure horse, so he carries a lot of tension in his body, especially in his back. With Chemaine's help, we've been inviting him to stretch down into the contact, but he's been historically too light in the bridle.
So now, we've gone from too light to too heavy. His neck was too short and his back was too tight. Now, his neck is too long, but his back is stretching. I think more transitions might help. To me, this sounds like progress.