From this interview check out the section 'Learn how computers work':

"So many developers don’t know how a computer works. Understanding computer architecture is extremely important, yet less than 1% of the people I see for interview know about their computers. If your focus is a high-level language, you still need to understand lower-level ones.

My advice usually is that you should at least know C, along with Python, Ruby, or Go, JavaScript, and a functional programming. You don’t need to master a lower-level language, but you should at least understand how it works, because it will then help you with other languages.

There are a lot of “developers” who are actually technicians of one framework in one specific language. But that’s no good, because what are you going to do in 2 or 3 years’ time? To be a good developer, you need to understand the lower-level languages as well as your own."

Then the section 'How to recruit the best developers'...

I try to think about it in these terms, if someone can show they understand, or it can be explained in a way that they will understand how computers and programming works and they can explain how they'd approach a problem, then they're probably worth investigation. Unfortunately willingness to learn can be easily feigned in interviews to secure a job. One problem that I've come across in recent years is that people seem to have completed courses covering a specific tool or technology, python or whatever, and are either unable or unwilling to learn more of the fundamentals or other aspects of technology.

Another problem is that people conducting the interviews often don't have a clue themselves, and are keen to rush through the process when there should be more focus on attention to detail.