Delusions probably rooted in reality, it's just severe. If one knew everything that everyone on this planet knew he wouldn't function in reality as someone who had a more segregated way. I think the filter goes and the person with psychosis gets what's relevant to the truth of there self minus the part that relates to reality in the conscious area of the mind.
Saying that, my delusion if you want was essentially that the world works a way other than that which most think it does and there was simply this with some chosen creative license of vampirism and reincarnation. Some grandiosity, some odd behaviour, some reference, yet all of it was relevant to my inner self but holy ###$ did medication help. It also killed my creativity and physical energy expression.
Delusion should be analysed if its a problem. You probably know pre-consciously what it means, but when thinking about it with language and societies lies it gets mixed into your projection it gets ###$ up.
No one's crazy anymore.