I could not agree more, it's rare to write a program where you know all the dependencies, libraries you will use and the overall effect to other parts of the program by heart. So, gradual design process is best.

I would point out, though, that that part also touched understanding requirements, which is many times a very difficult process. We might have a technical requirement conjured, by someone less knowledgeable about the inner workings, from a customer requirement and the resolution of the technical requirement may not even closely address the end-users' use-case. So, a lot of time also goes into understanding what it is that the end-users actually need.