We're accustomed to thinking of our world as really fast moving with constant technology turnover, but computer programming languages turn over at maybe twice the speed of human generations. A lot of the features that HN posters, including me, simply can't imagine a language without have yet to penetrate the top ten list of current programming languages at all.

My point isn't that this is wrong, but just to suggest that people's mental models incorporate the idea that programming languages actually move pretty slowly. There's a constant froth of undergrowth in the forest, but it takes a long time to establish a tree, and a long time for it to be supplanted by another.

And it was a mistake in all of them.

"I call it my billion-dollar mistake…At that time, I was designing the first comprehensive type system for references in an object-oriented language. My goal was to ensure that all use of references should be absolutely safe, with checking performed automatically by the compiler. But I couldn’t resist the temptation to put in a null reference, simply because it was so easy to implement. This has led to innumerable errors, vulnerabilities, and system crashes, which have probably caused a billion dollars of pain and damage in the last forty years." – Tony Hoare, inventor of ALGOL W.