I've found it doesn't always work that way. For instance, we have a legacy homebrew billing system that's a Lovecraftian nightmare of procedural PHP batch pipel

I've found it doesn't always work that way. For instance, we have a legacy homebrew billing system that's a Lovecraftian nightmare of procedural PHP batch pipelines. We're all eagerly looking forward to just replacing it wholesale, but in the meantime nobody delves into it, partly to preserve our sanity and partly because nobody wants to be marked as "the guy who knows it best" and condemned to maintaining it. All the original developers on that part of the system quit months or years ago, but we have the last of them on retainer to recover it from its failures. That's the guy we couldn't lose.