Imagine if people in 1700 saw their lives the way we'd see them. It would have been unbearable. This denial is such a powerful force that, even when presented with possible solutions, people often prefer to believe they wouldn't work.This is a very nice way to explain the issue, so I shall elaborate. People have, since the dawn of humanity, opposed new ideas that would reveal their lives as flawed and lacking and even miserable. This leaves two viewpoints we can take about the present: we are at the end of human progress and our lives have no serious flaws, or it is like 1700 and we are in denial about many problems.
Believing we are the best the Earth will ever offer goes against the facts. Everyone has problems. That's why it's possible to get a job as a psychotherapist or councilor. Saying there will be no more progress is really saying whatever problems we have now cannot be solved. Why say that? Because then our suffering isn't our fault. It might be possible to argue that some of our problems are insoluble, but certainly not all or most of them.
That leaves the other option: just like in 1700, we are in denial. I think this is broadly the case. When we say that temper tantrums are an inevitable part of parenting, that is not because there is no possible way to avoid fighting with our children, its because we don't want to see ourselves as failures. When we say children do bad things because they are children, that is avoiding facing the fact that we could have given better advice. (Some problems like that aren't foreseeable, but certainly some are.) When we say that "love hurts", we are denying that our own approach to relationships hurts us. When we divorce and insist vehemently that our partner is an evil bastard, we have to: if he wasn't a lying manipulator then it would have been possible to see the flaws in the relationship in advance. We didn't choose the wrong person, he tricked us! In all these examples we might be blameless, but sometimes there is something we could have done better, and assuming it might be partially our fault will help us find that out.
I want to move past this to a kinder view that expects mistakes and problems, and sees finding them as a positive step. We should feel good about discovering we were wrong: now we have a better shot at being right next time. Or if there won't be a next time for us, at least we could tell our children. And if it's important enough, we could write a book and tell the world.
We all have a lot of bad ideas. That's understandable. And it's excusable -- no, better than that: we don't need any excuse at all. But let's at least get one thing right: we aren't perfect. Most of the problems we face are caused by human mistakes. That's the most optimistic belief we can have because humans are capable of correcting their own mistakes.