How to prevent failure from introduced changes?
This is pretty deep in to "opinion based" but here goes:

While most definitions of "DevOps" are independent of specific tools and techniques, it is very often combined with things like test automation (e.g. Jenkins, Travis-CI) and deployment automation (e.g. Chef, Capistrano, Kubernetes). Those two together act as a forcing function to push up quality levels of software by making it both easier to use tests to ensure things don't break and making it easier to fix breakages when they do occur.

That said, I really doubt that number captures the full story. Like so many things, "software quality" is easy to talk about but difficult to define.