Earlier quoted context omitted.
This Never happened to me in 5 years of arch. I always considered this a hoax. How did Arch break?
To name a few: when systemd was introduced; when there were changes made to the file structure (moving everything to /usr); when kde4 was replaced with kde5. And there were more issues, I just don't remember all of them. Reading the news before the update could have helped sometimes but I don't do that every time I execute `pacman -Syu` for various reasons; and sometimes problems are unexpected or just bugs fixed on…
If you don't subscribe to the Arch news feed, you're taking a chance on every upgrade, that your system will not boot correctly.