This is sort of a 'turtles all the way down' sort of issue. You could also say:

> Learn assembly and the rest will come

> Learn binary and the rest will come

> Learn the fundamentals of electricity and the rest will come

...

I think learning the layers below which you typically operate can be beneficial; however, I think the patterns and ideas ( semaphores, scheduling, etc. ) are probably the most beneficial part of an exercise like this -- not the actual C language.