There are a number of accounts of that sort of situation floating around the Internet; it's not necessary to acquire the scars personally. As to how we get into those situations, I suspect that the universal path would be an erroneous 'rm -rf' command affecting the /bin directory.

  http://www.terminalinflection.com/negotiating-a-damaged-linux-filesystem-using-only-shell-builtins/
  http://eusebeia.dyndns.org/bashcp
  https://news.ycombinator.com/item?id=1212051