In order to avoid negligence it was told that breaking a mirror bring seven years of bad luck. That was simple scare tactic.
A variety of remedies are available to break the spell of misfortune. The Romans are also responsible for little known measure for avoiding the curse useful for anyone who breaks a mirror. The luckless who accidentally break a mirror, and does not wish seven years of ill-lack, must take all the pieces of the mirror and bury them in the moonlight, or take all pieces and throw them into running water, or pound the broken mirror into tiny pieces so that none of them can reflect anything ever again.