Early on in Janet Reitman's Inside Scientology: The Story of America’s Most Secretive Religion:
Scientology, as its critics point out, is unlike any other Western religion in that it withholds key aspects of its central theology from all but its most exalted followers. This would be akin to the Catholic Church telling only a select number of the faithful that Jesus Christ died for their sins.
Later, in the chapter “The Seduction of Tom Cruise”:
Cruise, in the meantime, had reached OT 3, the vaunted Wall of Fire. For seven years, he’d waited to discover the hidden truths that he’d been promised would change his life. When he did, he had what many former Scientologists say is not an atypical reaction — “He freaked out and was like, What the fuck is this science fiction shit?” as Marc Headley put it — and he took a step back.
“From my recollection, Tom went kind of crazy when he reached that level,” said Karen Pressley. “You have to remember that this was before the Internet became popular, and everything about Scientology was still veiled in secrecy. So as a dedicated Scientologist, following the roles, he would have never heard of Xenu, body thetas — any of that stuff. Finding out that this was what Scientology was about I’m sure came as quite a shock.”