But Spiritualists have an easier time with it.including unlocking the shroud. Only materialists have problem with that.
If you're not spiritualist, your chance to find Psionic Theory is reduced by 50%. If you're Fanatic Spiritualist, it's multiplied by 2 instead. So Fanatic Spiritualists are 4 times as likely to find it than non-spiritualist empires if everything else is the same.
Most other Psionics-category techs work similar - each having x2 and x3 modifiers to spiritualists and their fanatic variants.