What's the Difference Between a Delusion and an Illusion?

We evolved to have negativity bias for really important ecological environmental evolutionary reasons, right? In the same way that we have various biases about the way our vision processes the world around us or our sound identifies objects of different sorts. This is the delusion I'm talking about and of course it's an extremely useful helpful delusion that helps us turn food into adults. So it's not that this delusion is somehow useless or wrong, it's just not the whole story. And in terms of being a human being there's certain things about this delusion that can be painful and destructive.