For all Jews, the 10th of Tevet, is a day of fasting, mourning and repentance. Tevet 10 or Asarah BeTevet is also the day selected as a "general Kaddish day" for the victims of the Holocaust whose date of death remains unknown. Although work is permitted we do not eat food or drink any liquid from just before daybreak until nightfall. We also add Selichot and supplements to our regular daily prayers.
On the tenth of Tevet, the armies of the Babylonian emperor Nebuchadnezzar laid siege to Jerusalem, leading to the fall of the city. Thirty months later the walls were breached and on the 9th of Av (Tisha B'Av), Solomon's Holy Temple was destroyed and the Jews were exiled to Babylonia for seventy years.
For Orthodox Jews the destruction of the First Temple was the beginning of the end for the Jewish people. The Second Temple may have exceeded the First Temple in magnificence, but it did not have the holiness of the First Temple. Nebuchadnezzar had looted the Holy Vessels, and the miracles of the First Temple were absent.
May you have a meaningful fast.