in order to change an existing imagined order, we must first believe in an alternative imagined order. - Yuval Noah Harari

As far as we can tell, from a purely scientific viewpoint, human life has absolutely no meaning. Humans are the outcome of blind evolutionary processes that operate without goal or purpose. Our actions are not part of some divine cosmic plan, and if planet Earth were to blow up tomorrow morning, the universe would probably keep going about its business as usual. As far as we can tell at this point, human subjectivity would not be missed. Hence any meaning that people ascribe to their lives is just a delusion. The other-worldly meanings medieval people found in their lives were no more deluded than the modern humanist, nationalist and capitalist meanings modern people find. The scientist who says her life is meaningful because she increases the store of human knowledge, the soldier who declares that his life is meaningful because he fights to defend his homeland, and the entrepreneur who finds meaning in building a new company are no less delusional than their medieval counterparts who found meaning in reading scriptures, going on a crusade or building a new cathedral.
So perhaps happiness is synchronising one’s personal delusions of meaning with the prevailing collective delusions. As long as my personal narrative is in line with the narratives of the people around me, I can convince myself that my life is meaningful, and find happiness in that conviction.
This is quite a depressing conclusion. Does happiness really depend on self-delusion?

Social cooperation is our key for survival and reproduction.

Humans have this remarkable ability to know and not to know at the same time. Or more correctly, they can know something when they really think about it, but most of the time they don’t think about it, so they don’t know it. If you really focus, you realise that money is fiction. But usually you don’t focus. If you are asked about it, you know that football is a human invention. But in the heat of the match, nobody asks you about it. If you devote the time and energy, you can discover that nations are elaborate yarns. But in the midst of a war you don’t have the time and energy. If you demand the ultimate truth, you realise that the story of Adam and Eve is a myth. But how often do you demand the ultimate truth?