The filesystem table, or more commonly known as
/etc/fstab, is a system configuration file, which is parsed by
mount during boot, and misconfiguration or typos can render the system somewhat unusable.
By default on Debian and Ubuntu systems, the root partition has the
errors=remount-ro option set, which indicates that if the mount encounters any error, it should only remount the partition as read-only, to prevent damage. In that case, for example, many applications will stop working, unexpected behaviour will be present, among other issues.