IME the best abstractions hide the underlying complexity by default, but allow you to "pop the hood" when necessary. The more this exposes the guts of the underlying implementation details, the better (though obviously that comes with tradeoffs around changing underlying impl details, although I think as an industry that we over-index on that too much, which leads to exactly this problem).

Go's compiler intrinsics immediately come to mind here. They allow you to easily write Go functions in native assembly, without CGo, for hot code paths. We get the benefits of a high-level language with a fat runtime, but can easily drop down to assembly when we need to.