Complex reasoning behind this but if you're 99.9999% sure of something (via a valid process of experience and reason of course) outsiders all disagree with and you're suddenly presented with evidence to the contrary it's far more likely you're in a falsified simulation than wrong
Imagine, for instance, believing in altruism, and suddenly having an introspective moment where you realize your motivations are pure evil straight out of an Ayn Rand novel. If hidden superficial depths suddenly appear in you they are probably someone else's imposed imagination.