Don't tell me it's impossible, tell me "I can't do it"... We had architecture sketches (informal, but highly taylored to show the gist of a system) that stayed

Don't tell me it's impossible, tell me "I can't do it"... We had architecture sketches (informal, but highly taylored to show the gist of a system) that stayed valid and were used from after the first prototype to well after release, over a course of more than five years. It was a system of six embedded processors, 2 FPGAs, 5 different bus technologies, (luckily only) two different endianesses and coding and debugging would have gone horribly wrong without that overview sketch of just enough detail. There are cars in your town that drive around with it for a dozen of years now.