I say that we aren't. And given that, you are better off believing the lie that helps you or makes you feel good instead of the one that hurts you, assuming both have the same predictive power.
So I appreciate your perspective as I think it aligns with mine.
I believe that for situations where a single human has enough information and ability to ascertain the truth, most humans deliberately will not make a beeline for the truth. They sort of veer off to the side towards a half truth that better suits their situation. None of this is a conscious choice though.
Self deception is completely orthogonal to our ability to ascertain the actual truth. As I said even if we were magically gifted this ability, most choose not to use that ability.
Of course this quality lives on a gradient, some people are really good at self deception, others are really bad at it.
I mean who cares if some guy running a convenience store or writing an email client thinks the world is flat?
Maybe we just need a small aberrant percentage of the population so there will always be a few people "shorting" the status quo for cash and occasionally preventing extinction.
It's not just this. It seems as though lying to oneself is so pervasive that it is likely a biological advantage.
Meaning not only is obsession with the truth not advantageous but it's actually disadvantageous while the opposite self deception is actually normal and highly beneficial such that this trait has been naturally selected to persist.
We didn't need to be perfect to get to this point. Just good enough to beat the environment and the other meat sacks.
Predictiveness of a mental model is the the closest we can get to understanding reality.