That day is the feast of the last one of the hail-men family – sometimes interpreted as a brother, Vido, sometimes as a syster - Vida. Only those who have celebrated the other three brothers are allowed to participate in that last feast.
The traditional belief is that it is Vido who punishes sinners. This explains the old Bulgarian saying "Vidovden will come!" Therefore, if the feast is celebrated, God will not see the sins and they might be left forgotten.