[wilun]

Are you even trying?

A random search tells me that "The mean DD for the studied sample of projects is 7.47 post release defects per thousand lines of code (KLoC), the median is 4.3 with a standard deviation of 7.99." ( https://ieeexplore.ieee.org/document/6462687/ )

So clearly if you are careful and use state of the art practices, this is very doable.

Not only this is doable, but various individuals and teams in history have been able to reach way lower defect densities. Hey, for all practical purposes, TeX is bug free, for example.

If you are not able to write 100 lines of useful code without a bug in it (not in an infallible way, but at least sufficiently often enough), maybe you should simply study and practice to get that ability.

[izzydata]

Those measurements inherently make no sense as you can't know unknown unknowns. Sure, for all intents and purposes if you never encounter a particular defect in a billion years of usage then a bug may as well not exist, but that doesn't mean it doesn't.

[wilun]

Those measurements inherently makes more sense than hand-waving; and although mathematically I agree with you, the world is not mathematically pure.

Regardless, I stand that implying that it would be exceptional to be able to write 100 lines of bug-free useful code is ridiculous. I'm not stating that it is easy, nor that most of chunks of 100 lines are written like that. Just that not only this is possible, but this is accessible. Now depending on the field it might be more or less difficult, but in general I suspect there are tons of chunks of 100 lines that have been developed correctly on the first try, and those metrics tends to, non-formally I concede (but if you dig enough what is even formal enough?), weight more in favor of my view point than in favor of the difficulty level being astonishingly high.