OK, the first ten or so things. In https://www.amazon.com/gp/product/0345409469/002-3736669-4481603?v=glance&n=283155", Carl Sagan wrote these much quoted words (my bold): Suppose the "almost no one" were to become one-tenth of what it is today; what would the first dozen or things be that would "blow up in our faces"? Why choose those ~10? How quickly would the (massive) failures occur? What if it were 1%, 0.1%? What about exactly 'no one'?