Some are VERY RIGID about their beliefs. No wiggle room at all. Others are flexible. HOW do they KNOW what is unknowable till they die?

That's like having the ability to foretell the future. Some seem to believe they KNOW. How that is I do not know. I also don't know how many millions believe in KARMA and REINCARNATION. We believe what makes sense to us and ignore what doesn't. Different strokes.