You don't need to understand how the whole system works. What you need to understand is the API's in-between the sub-systems. Another way to put it is that th

You don't need to understand how the whole system works. What you need to understand is the API's in-between the sub-systems. Another way to put it is that the architecture is the API's. You can in principle throw away and re-implement the sub-system for a specific API without understanding the rest of the system. I am saying in principle because in practice API's are typically under-specified leaving out important side effects.