[newt]

Ok, that at least makes sense. But ... sudoku is a puzzle - you don't (or at least I didn't) get there by iteration and testing, you get there by a flash of insight - "if I try searching like this, I might be able to end up with a solution to any sudoku board" and few hours later I knew I was right. In that way, it is unlike almost all large-scale software development.

Agile can't generate insight from nothing, it's not a silver bullet. But at least if you have some unit tests around your cool new code, you know that you won't accidentally break it later.