I think people believe in heaven because they don’t like the idea of dying, because they want to carry on living and they don’t like the idea that other people will move into their house and put their things into the rubbish.
Happiness in this world, when it comes, comes incidentally. Make it the objet of pursuit, and it leads us a wild-goose chase, and is never attained. Follow some other object, and very possibly we may find that we have cought happiness without dreaming of it.