Yesterday I went to upgrade Joomla from my old version about 6 months old to a newly released version. As I have not managed this site in too much detail outside of the occasional post, I did not think to back everything up as something could go wrong, and as the story goes, I upgraded with the auto update tool and the upgrade failed in a few parts.
Ended up going to a Joomla forum to see if they could help but they pretty much said the same things I tell customers when they call with questions or major changes need to be made to the system, "Keep backups. Know what you're doing when making changes. Document any changes made and error message. etc."
Thankfully though after a few hours of headache but mostly waiting, it's all back up, and I have a backup stored safely just in case any updates pop up soon!