I still find that these are not easy concepts to explain to people outside of software development. Yes, they start to get it after 1 or 2 projects, but I can't

I still find that these are not easy concepts to explain to people outside of software development. Yes, they start to get it after 1 or 2 projects, but I can't help but wonder that there is something more fundamental here. Something along the lines of, "I know what the finished product is supposed to be, why does it have to be broken down into incremental deliveries?" I think that non-tech people often see it as a kind of watering down of their vision.