Agreed on both points. I doubt Sybil forgot it. In his case it's more a matter of perception; the ability to see things as they truly are.
Mental illness is like seeing the world through a fun house mirror. They believe the distortion is real. Sybil, and a few other JPP Trumpers for various reasons, are unable to perceive the truth.
It's a matter of mental processing just like dyslexia*; we all see the world through almost identical eyes and, for the most part, we all process what we see the same way. To do much less wouldn't be advantageous for a tribe of humans in the long run. Other predators, either two or four-legged, would have a major advantage over those unable to effectively reason.
For the mentally ill, the distorted processing depends upon their specific illness(es). The factor they all have in common is that
reality is distorted in their mind.
In short, Sybil won't agree or see your point because it's impossible for him to do so...at least without proper treatment.
https://www.mayoclinic.org/diseases-conditions/dyslexia/symptoms-causes/syc-20353552
This isn't "riled up", sir. This is me exploring the mind of a severely mentally ill person. Best of luck and a happy life, but you'd be better off with seeking the counsel of friends...real ones.