> "I have only proven [my code] correct, not bug free."

> -- Donald Knuth (if I recall that exact quote correctly)

Just because you have proven the correctness of your code, that does not mean that it is infallible. Especially -- as a lot of HN users point out -- there's intricate complexity that is likely to cause erroneous behavior if several interfaces/complexities get combined. And those might be caused, for example by a 'user' setting the driver to 'db.backend.sqlite' instead of 'db.backend.sqlite3'; and then you have suddenly an unexpected configuration.