Oh yeah. I've spent my last (almost) three years (thankfully they're over now) working on that kind of codebase and it's been an absolute nightmare. The very fe

Oh yeah. I've spent my last (almost) three years (thankfully they're over now) working on that kind of codebase and it's been an absolute nightmare. The very few original(-ish) authors still on the team were generally very helpful, but the codebase was huge, some of it was bought from someplace else (so there was no one to explain anything, and no documentation because of course not), and the team had been downsized in the course of time. Patching it up with contractors, needless to say, didn't quite have the stellar effect that management had hoped it would have. Three years later I was still struggling to figure out even the most basic of features. It would regularly take me days, sometimes even weeks to fix trivial bugs. The convoluted code definitely didn't help (message passing between several processes, 4000-line functions...). There were a lot of features that I could barely use, let alone debug. I had no mental model of the code at all. Figuring out where my mental model didn't match reality was pretty much out of the question under the circumstances -- and my only source for creating a mental model of the code was, well, the buggy code. Thankfully, I also worked on other things during these three years, so my sanity is still mostly intact. But that thing was really terrible.