Fun story:

I once was in some kind of SSH-ception, my machine and two remote machines where the same, as in the username and hostname (local name) where equal. All with and Hitachi 500 GB disk.

I was going to nuke the remote machine 1, so later that day I would rebuild the system and all that good stuff, so it would be equal to remote machine 2.

I check the disks and see that it is what I expected, and proceed with the so called "sudo rm -rf /".

Turns out, in my madness, I was doing this on the remote machine 2, not on remote machine 1 (too many terminals), and after I pressed the button and 5 minutes are passed, I realize my mistake...I had just killed a big part of some research I was doing for college (100 or so simulation files, 2GB each).

LESSON: Always triple check your drives and sessions.

P.S.: Something similar happened with me once doing dd to make a ubuntu bootable flash, I ended up erasing 800GB of backup files.