The beauty of programming is abstraction - you write a function to do one thing, do it well, and then you can abstract that concept away and reuse that abstraction. Although it's only an abstraction - a container is "like" a lightweight VM, and you can use it like that until it doesn't act like a lightweight VM. In which case, you have to dabble one layer deeper just to understand enough to know why the abstraction of your layer isn't a perfect analogy.
In which case, if you're looking for an expert in layer n, then basic knowledge of layer n - 1 might be a decent proxy for expertise
Reminds of this xkcd: https://xkcd.com/435/
The beauty of programming is abstraction - you write a function to do one thing, do it well, and then you can abstract that concept away and reuse that abstraction. Although it's only an abstraction - a container is "like" a lightweight VM, and you can use it like that until it doesn't act like a lightweight VM. In which case, you have to dabble one layer deeper just to understand enough to know why the abstraction of your layer isn't a perfect analogy.
In which case, if you're looking for an expert in layer n, then basic knowledge of layer n - 1 might be a decent proxy for expertise