Why Do We Cry?

We are well aware that this Sunday, the ninth day of Av, Tisha B’Av is the saddest day of the year. We sit on the floor until noon of that day and we recite Kinnos, special prayers evoking the tragedies of yesteryear which actually remind us of the calamities that have befallen us in every generation. We mourn the loss of the Beis HaMikdash which was destroyed a couple of thousand years ago.