Scrum "by the book" has a lot of material on the edge cases. How you handle almost every case that can happen in a software development team. So you can follow it like a workflow. Something unusual happens, you look in the book, do what it says. It's flaws are fairly well documented and understood, too. That's what I mean by being "on your own" if you don't follow it. At that point you can't just use a book to figure out next steps. You have to actually talk it out and use your brain to figure out what to do, because its unlikely your internal process has as much documentation around every single "paved paths".
It's also just a process. What does it mean not to find success here? If you ship broken software, it's unlikely to be because you didn't move the right ticket in Jira.
If you implemented Scrum "by the book", the likely "failure cases" are more things like people refusing to actually follow the process because they find it to be a waste of time, the overhead is too high, people are sick of looking at the book, etc.
Don't get me wrong: I very much dislike Scrum and you'll never see me push for it in a team. My point was merely that if you take an "On rails" experience like Scrum, and tweak a few little things, you lose on almost everything. The books no longer apply. When the entire point of this particular process is basically the books and documentations, doing "Scrum but not quite" really kills the point.