Not attempting a full rewrite of a significant codebase is excellent advice because it's usually the right advice. That's not to say that it can never be succe

Not attempting a full rewrite of a significant codebase is excellent advice because it's usually the right advice. That's not to say that it can never be successful, just that the circumstances in which it will are sufficiently rare that it's usually worth discounting relatively early on. In >20 years of dev experience, I can only think of one occasion where I successfully did a big bang rewrite i.e. tore down an application and restarted it with an equivalent system that had approx zero common code. In that case, it was a C++ program that wouldn't actually build from clean. A lot of the code was redundant as the use cases had morphed over time (and/or weren't ever required but were coded anyway) and most changes were stuffed into base classes as it was effectively impossible work out how objects interacted. Releases took about 3 months for about 2 weeks worth of dev. Initially, I didn't plan to rewrite it. When I realised I couldn't understand what it was doing, I took a step back and worked out what it should have been doing, assuming that I could map one to the other. What I found was that, at heart, it should have been doing something fairly simple but that the original "designers" had thrown the kitchen sink at it and its core function was lost in the morass. I also came up with a way of making it easy to show that the new system was correct more deeply than just tests. This gave me, and folks I needed to convince, a lot more confidence that a rewrite made sense than would normally be the case. In summary, it was quite a rare set of events that led me to the conclusion that a rewrite was the right direction: the existing system being a complete basket case, my happening to have a lot of domain expertise, the problem space turning out to be relatively simple and finding a way to "prove" correctness, all contributed. I doubt I would have made the same decision if any of them were different.