I never questioned that, I of course use the abstractions myself, when convenient. Where have you received an impression that I promote "actual Thread instance"

I never questioned that, I of course use the abstractions myself, when convenient. Where have you received an impression that I promote "actual Thread instance" or the use of any specific language construct explicitly? I haven't written anything like that. However, even if the abstractions exist, that doesn't mean that understanding the lower levels, or what is abstracted and what not, is not necessary. Those who don't know what actually happens often have wrong expectations, and design their code based on them. Then only later it turns out that the expectations were simply wrong, and not that the OS or the libraries or the languages made some false promises. Often, the most interesting information is not what are the abstraction primitives but what from lower levels is not covered by these abstraction primitives, or how these abstraction primitives map to which lower levels.