We have all done it if you work long enough. I blew up my Debian Linux system with an incredibly stupid mistake breaking the whole system. It is actually one of the questions I have when interviewing someone. “What is the worst mistake you’ve ever made?” And if they admit one, the follow up question, “What did you learn?”
I renamed my /usr directory to /usr-root with a mv /usr /usr-root as the root user. I knew I was treading on dangerous ground so I fortunately had two ssh console sessions up and both running as root. The goal was to migrate the /usr to separate storage to recover space for the very full root disk.