I accidentally the config file
Yes, today is the day that I made a fine boo-boo. A shameful one, to be honest.
I was deploying config files for the monitoring software and got lazy - I overwrote files instead of moving them or renaming them...all because I wanted to get that last little bit done before I left for the day.
Of course it turns out that some esoteric command was in the files. Not mission-critical, but I'll be spending time in the backup software tomorrow (assuming the servers were ever backed up) trying to figure it out. Or re-writing the command from scratch. Ouch.
The amount of time it will take to rename the files versus restore from backup can be described in orders of magnitude. Honest to goodness - at least this project is almost over.
Lesson: Even if you are 100% certain you'll be okay overwriting a file - move or rename it for insurance, because restoring from backup is tedious and painful and sometimes an endeavour in panic.
Sub-lesson: Are you in a hurry to go somewhere? Are you simultaneously working on production systems? Just stop. Stop right now.