I recall trying to check if there was an OpenBSD image available for install, going to the VPS re-installation panel and messing things up there. I ended up wiping my server with an unintended clean install of the same OS I had.
Gladly enough, it was a replicated cloud VPS and they did have a backup. I blessed ticking the "high availability" box.
Morality: next time just send a ticket to support asking if they support a certain operating system.
I accidentally deleted my school assignment database file that took me about a week to complete and my recycle bin was also cleared. I was relentless to recover that file and so I tried about five data recovery software until I was able to recover it. That moment has taught me to always backup my important files using my email inbox or a usb drive.
Wiping the entire site's entire database, including the users, some of them actually paid for some gimmicks I put to sale and I received tons of complaints. I refunded their money, but that wasn't the biggest issue for me: I had to start all the site again from scratch. Oh, god! Another 3 months of tediously-working because of a single unresponsible maneuver.