Back in the days mirrors were rare, expensive and treated with care. Breaking one would certainly have been considered unlucky. Apart from that it was just another example of the weird tradition of trying to scare people into doing certain things.
Friday 13th, black cats, breaking a mirror, walking under a ladder, opening an umbrella inside and finally putting shoes on the table.
There is no such thing as an unlucky day. Although, there are unlucky things such as the devil.
unlucky
unlucky
Not lucky; not successful; unfortunate; ill-fated; unhappy; as, an unlucky man; an unlucky adventure; an unlucky throw of dice; an unlucky game., Bringing bad luck; ill-omened; inauspicious., Mischievous; as, an unlucky wag.
All cards that do not target (Ex. Mirror Force, Lightning Vortex, Fissure, Smashing Ground, Bottomless Trap Hole, Hammer Shot).
Smashing Sebastian was born in 1974.
Smashing Drive was created in 2000.
Smashing Drive happened in 2000.
The Smashing Pumpkins was created in 1988.
The Smashing Pumpkins ended in 2000.
Smashing the Serene was created in 1998.