When you are in that business you need to be very intelligent which limits the scope of self deception a bit. But a person can actually have many contradicting and self contradicting opinions at the same time. So it is possible to be highly religious and pray to the Lord every hour and at the same time commit crimes against all ten commandments in between. When enough people follow you and give you much positive feedback it can convince a person to actually feel more and more as if they really have powers they started to fake initially. When your life is based on propaganda and fake that backfires usually the longer you fake and do tell fake. Based upon that I guess that the longer they did it the more they tend to actually believe in their assumed predictive powers. So probably many if not the most assume they at least are powerful in deception if not prediction.