My point about software systems being less constrained than physical systems means that even ho-hum CRUD apps will likely have more unknown unknowns than a ho-h

My point about software systems being less constrained than physical systems means that even ho-hum CRUD apps will likely have more unknown unknowns than a ho-hum dirt moving project. Also, the task of stating the requirements for a software system is much more involved than stating the requirements for a bridge or tunnel. In short, I think there are very clear and tangible things that give software estimates a meaningfully higher uncertainty than other engineering disciplines.