Agreed, to a point. What kind of abstractions are sufficient, or useful? What happens when they leak? What happens when you build the wrong abstraction, and have to go back and build something slightly different from the ground up? What about when your abstraction works, but is so far removed from the actual execution environment that it's so slow as to be unusable?
Yes, abstraction is a wonderful, useful thing that lets us think and do all sorts of wonderful, useful things - our high level programming languages and networking protocols are abstractions over lower level programming languages and networking protocols (repeat a few times) which are abstractions over the physical hardware they run on, and that's great. But abstractions are never perfect, and what you don't know about the lower levels of the stack will bite you, which is a good argument for using as few and as thin abstractions as you can to get your thing done (reasonably ... I'm not about to write this comment in binary ASCII, say).
He mentions the point when the abstractions in the language are no longer sufficient. It seemed to me that this was more an argument in favor of using languages that are easily extended rather than languages full of abstraction with few options for extension. If you use a language like the latter, you'll still eventually reach a point where the abstractions aren't sufficient, but if you use a language like the former, though you'll reach that point sooner, you'll be better equipped to handle it.
Yes, abstraction is a wonderful, useful thing that lets us think and do all sorts of wonderful, useful things - our high level programming languages and networking protocols are abstractions over lower level programming languages and networking protocols (repeat a few times) which are abstractions over the physical hardware they run on, and that's great. But abstractions are never perfect, and what you don't know about the lower levels of the stack will bite you, which is a good argument for using as few and as thin abstractions as you can to get your thing done (reasonably ... I'm not about to write this comment in binary ASCII, say).