Hm. If it were so easy (refering to the first paragraph now) people would have thought of it earlier. And I think they did. As far as I know there were some badly working prototypes of printing presses before Gutenberg. Getting there is not all that hard. It's the little details that will get you in the end. Dozens of little things you have to figure out (or find out who figured them out before) in order to solve them. I would guess that any invention is full of those little details. Understanding the basic principle is easy. Getting the details right is hard.