I develop desktop and embedded applications, so do a different work than distributed systems engineers, but I wonder - do you often build systems from scratch a

I develop desktop and embedded applications, so do a different work than distributed systems engineers, but I wonder - do you often build systems from scratch and therefore need to have all this knowledge? Because in every job I've worked in the past 10 years, I landed in an established project, that was developed years ago, and my work was to maintanace and add new features. Most of these projects were too big and complicated for one person to know how they work in every detail - even the ones that were there for the very beginning always said something like "after all these years I don't know how half of the things are implemented". So, from my perspective, an interview question where someone asks me to design a complex system entirely on my own, in details, is just stupid, as I am pretty sure I will never do anything like that in my life. But maybe webdev is a different story?