From memory, he made those comments after he'd been working for a long time in C/C++. He's since seen that language like Haskell and Ada which enforce much stricter requirements have a huge benefit to developers; the inital extra work to learn the language pays off when you get used to spotting even more bugs before you write them because you've been punched in the head by the error messages in the past. You begin to think about code not just from a "how doI get this done?" standpoint, but a "how do I get this done properly, safely and clearly, and make sure the compiler will catch me WHEN I make mistakes". Fixing bugs at development time is vastly less expensive than in testing or after release, so the extra errots can easily be justified.