Here's a number for you: 1 Billion nanodijkstras.
What about the world where there is no spec for a finished version, merely different balances between effort, cost, value, marketability, usability, and so on...
This type of software needs to be correct all the time, every time. Adding a trivial feature, like adding USB support, isn't even a consideration (but if it was valuable it would be included in the next generation of the program).
http://www.ralentz.com/old/space/feynman-report.html
The section titled 'Avionics' is a good read for any programmer and relevant to Dijkstra's discussion (@ 13:00) of the software developed by IBM and used in the Apollo lunar module.
Perhaps I'm not smart enough to model accurately enough in my head, or perhaps not disciplined enough. I'd love to feel what it's like to think as someone else for a short while.
What "thinking" means to other people.
I think people vary in how much they can model in their head - but everyone has a limit. For me, the interesting question is how to work around that limitation.