(Normandy conversation regarding the heretic virus)
Legion: This heretic weapon introduces a subtle operating error in our most basic runtimes. The equivalent of your nervous system. An equation with a result of 1.33382 returns as 1.33381. This changes the results of all higher processes. We will reach different conclusions.
Shepard: So the reason they worship the Reapers is... a math error?
Legion: It is difficult to express. Your brain exists as chemistry, electricity. Like AIs, you are shaped by both hardware and software. Geth are purely software. Mathematics. The heretics' conclusion is valid for them. Our conclusion is valid for us. Neither result is an error. An analogy. Heretics say one is less than two. Geth say two is less than three.
By this analogy, indoctrinated people aren't wrong either...