In my experience, it's an unknown-unknown problem (don't know what we don't know).

Is it important you can recite cache eviction algorithms from memory? No.

Is it important you know there are such things as caches and roughly how they work? Yes. Because then you can quickly look up the details when/if you need them.

Is it important that you understand cache eviction algorithms well enough that you can look at a description of an algorithm and see how it applies to your system? Yes. And if memorising is the way you gain that ability, then memorising is what you need to do.

And what is it important for? Why, for making sure that your software makes efficient use of system resources. This is essential if you're writing application software that's used by other people – but if you're writing server-side code, or some one-a-month business-logic data-processing scripts, or code that's only ever going to run on five specific machines, it's not that big of a deal. I haven't needed this skill yet.

> I'm not sure it's always obvious to ourselves when we have.

Agreed. Some people would have to change employers in order to break through the ceiling, or to even see how they're limiting themselves. And for some of them: why would they?

Agreed. I can almost guarantee you that if you've written code that has any sort of performance needs at all (which describes most code) you've written something badly or suboptimally that you could have easily avoided or improved if you'd had a deeper understanding of the compiler or CPU. Every single one of us have.