It's certainly the case that I don't always know how the layer below works, i.e., how the compiled code executes in detail. But I have a mental model that's good enough that I can use the compiler, and I trust that the compiler authors know what they are doing and that the result is well-tested. Over forty years and a slew of different languages I've found that to be an excellent bet.

But I understand how my code works. There's a huge difference between not understanding the layer below and not understanding the layer that I am responsible for.