On the 10th of Tevet of the year 3336 from Creation (425 BCE), the armies of the Babylonian emperor Nebuchadnezzar laid siege to Jerusalem. Thirty months later -- on Tammuz 17, 3338 -- the city walls were breached, and on 9 Av of that year, the Holy Temple was destroyed. The Jewish people were exiled to Babylonia for 70 years.
Link: Asarah B'Tevet
Tevet 10 is observed as a day of fasting, mourning and repentance, in remembrance of the siege of Jerusalem. We refrain from food and drink from dawn to nightfall, and add the Selichot and other special supplements to our prayers. (More recently, Tevet 10 was chosen to also serve as a "general kaddish day" for the victims of the Holocaust, many of whose day of martyrdom is unknown.)
Links:
Learn about Tevet 10
Essays and Stories on the Holocaust
The Baal Shem Tov described life as a spiral staircase, constantly deflecting away from your target in order to attain it.
In Yiddish it’s called a “swindling staircase.” Some wise chassidim have pointed out a connection: Life swindles you into believing you are going in circles when really you are traveling higher each day.
This is the way of every true and lasting ascent: Just as you’re making some progress upward, you see yourself falling away and stumbling in the dark.
If you could see the whole picture, how all things resolve in the end, you would see how those periods of darkness and failure are truly steps higher and yet higher.
They must be. Because we did not create life.
G‑d did. And for Him, there are no failures—