Comment by harpiaharpyja

It depends. I've been stuck with a very large, very old, particularly awful legacy codebase before, and doing anything with it starts to resemble building the staircase.

Find the cause of a bug. Oh, but the fix isn't clear, because it turns out the "bug" isn't a programming error as it was - two people who had two slightly different but incompatible interpretation over the meaning and purpose of some subsystem (whose creator didn't document anything because hey, gotta meet deadlines). So now we have to decide what is the most correct way to resolve this while breaking the least amount of stuff... hmm, we could refactor this, separate that, give this a clearer purpose... oh, but surprise, it's tightly coupled to this, which is tightly coupled to that, which is tightly coupled to... FML.