To be fair, it said "an enormous amount of code", not "your entire app", but yes, the ability to add unexpected new features or make focused changes without touching more than a minimal amount of existing code is a very good smell metric of code quality. The problem is that for every dev who understands how to program like that, there are at least five, probably more like ten who don't, which means most of us are working on teams that produce a blend of clean code and, as you say, dog shit, so the feature request that requires stirring up all that shit is out there waiting for us, like it or not. The best we can do, when it hits, is try to at least improve all the shit that we touch in the process. Maybe some of it can become compost, I dunno, the metaphor breaks there, gonna have to refactor the metaphor.