Just fifteen minutes ago I realized that my script to refactor the primary file server (newly converted to ZFS) into more sensible datasets had an irritating detail wrong (a path element was being duplicated in some paths).
I said to myself "oh, I'll just roll that whole thing back to the snapshot I made 30 minutes ago".
Then I go "zfs list -t snapshot" and discover that my snapshot was holding onto 0 GB because I forgot the -r switch to make the snapshot recursive.
Oh, well. By some impossible-to-separate mixture of good management and good fortune, it turns out I had a set of (different) snapshots from the last two days covering all datasets in questions. I lost very little work (only scripts were executed against these datasets and I still have all the scripts).
My real screw up?
Back in my second co-op workterm job, I managed not to notice that a system I was backing up changed the order of the listed drives between two very similar screen requests that I made almost immediately one after the other. Unfortunately, on the second pass I selected the active system drive as the recipient of the system backup, picking from the position in the menu where the desired destination drive had appeared moments before.
I had become accustomed to my home system being deterministic in the order it listed things. My bad.
This is back at the very beginnings of the 4.77 MHz era, so my PC was actually not yet what we now know as a "PC" (its father had an S-100, and its mother had a itty-bitty CRT).
Thirty years later I still can't type dd of=/dev/ada3 without making three trips to the metaphorical bathroom.
Whenever I type a disk-level dd command, I leave the sudo off, until after the third proof-read and several console consultations in which at least two different programs give me the same view of the drive name.
In dollar costs I couldn't say. In psychic cost, it's indelibly etched onto my permanent record.
I had a co-worker once (EEng) who claimed that as a junior intern during the late 1990s back when laser gear for fiber optics was all the rage, he routinely fried extremely delicate $2000 DUTs while the old hands just shrugged their shoulders. Dotcom dollars. Who really gave a fuck? It was considered barely worse than ruining a nice chair.