Why on Earth? Broken mirrors.
Why do people say a broken mirror means seven years’ bad luck?
In many ancient cultures, mirrors had a strong mystical significance - they were thought to offer glimpses into the viewers’ soul. Break the mirror and you break that link, inviting all sorts of bad luck. Why seven years? Seven is the most mystical of numbers - it’s a prime which is also the sum of two Pythagorean lucky numbers, 3 and 4. And does breaking a mirror really mean you’ll have bad luck? In a word, no.