I can't tell you how many times I have been told "my horse can't be ridden bitless. I tried it once and he didn't listen/bucked/ran away/was generically bad so now I'll never do it again, even if he could be more comfortable."
Lucky for me, Bailey showed me exactly why this "I tried it once and never again" mindset isn't valid. We began seriously working on backing up during our last ride, and despite my using very gentle hands with just a snaffle, I noticed her becoming more and more stressed about the bit. It got to the point where I would even close my fingers and she would hyperflex and begin spinning her haunch out to the left, despite even rein and leg pressure, while anxiously chomping the bit constantly.
I spoke with her owner, and I asked if I could try her bitless. She had a sidepull I could use, so we tried it out. While she was responsive on the ground, the lack of any body language in the saddle meant she had a bit of a panic when I first got on. Above you can see I ask her to back 3-4 steps, then she begins spinning, flipping her head and rooting. This happened several times within the first 10 minutes, but I would just continue doing my best to be clear. Every time she would freak, I would stay calm, regain control, then try again and reward her BIG TIME for the correct answer. No getting mad. No picking a fight. Just consistent positivity.
After about 20 minutes of consistent practice, all at the walk and trot, she was stopping from my seat, rocking back, and lightly backing straight and calm when asked. She even began to tuck her butt into the stop just a bit. Was she flexing down on the vertical and racing backwards? Nope. But she was calm, listening and positive.
People get so caught up in how the horse looks, and expect them to grasp everything right away. Teaching horses is a process. With a smart horse like Bailey, it only took me 10-15 minutes to help her understand new cues. For other horses it may take a week or a month.
My point is this: claiming something can never be done because you couldn't achieve it in one ride is ludicrous in all other facets of riding, so it applies to bitless riding as well.