[rednafi]

Every refactor attempt starts with the intention of 100% coverage.

No one can predict how efficacious that attempt will be from the get-go. Eventually, often people find out that their assumptions were too naive or they don’t have enough budget to push it to completion.

Successful refactoring attempts start small and don’t try to change the universe in a single pass.

[daxfohl]

Sure, but do some due diligence. I just say that because I've seen a couple cases where someone does a hack week project that introduces some new approach that "makes things so much cleaner". But then after spending a couple months productionizing it and rolling out the first couple iterations to prod amid much fanfare, it becomes evident that while it makes some things easier (oftentimes things that weren't all that hard to begin with), it makes other things a lot harder. So then you're stuck: do you keep pushing even though it's a net negative, do you roll back and lose all that work, or do you stall and leave a two-headed system?

In most of these cases, a few days up front exploring edge cases would have identified the problems and likely would have red lighted the project before it started. It can make you feel like a party pooper when everyone is excited about the new approach, but I think it's important that a few people on the team are tasked with identifying these edge cases before greenlighting the project. Also, maybe productionize your easiest case first, just to get things going, but then do your hardest case second, to really see if the benefits are there, and designate a go/rollback decision point in your schedule.

Of course, such problems can come up in any project, but from what I've seen they tend to be more catastrophic in refactoring/rearchitecting projects. If nothing else, because while unforeseen difficulties can be hacked around for new feature launches, hacking around problems completely defeats the purpose of a refactoring project.