I think some self-deception is essential in the sense that some things are true but you don't necessarily want to be aware of them all the time. Death being the obvious example.

Like Karen, I choose to believe most people are good FSVO good, even though I don't know if it's true or not. If it was absolutely proved not to be true, I suppose I'd stop believing it, because I don't think I can really believe things I *know* aren't true. But absolute proof seems unlikely so as long as there's wiggle room I'd try to keep believing.

I have a belief that things turn out for the best in the end, but I don't believe it's objectively true as such, it's just something I feel comforted by. But it seems good for my mental health to have that belief.