We say in the bracha of the Haftora - "רחם על ציון כי היא בית חיינו" - Have mercy on Tzion because she is the house of our lives.
After Tzion was destroyed, we lost the source of our lives. We are alive on some level, but are sorely missing TRUE life.
Let us say a person grows up in New York City. He is USED to breathing polluted air. [No offense. I love New York, but the air is very polluted.] One day, he goes to a town in Switzerland where there is almost NO pollution. No cars or other polluters. Good, pure air. He breathes. Ahhhhhhh!!! A taste of paradise. He never realized what he was missing.
We are COOOOOLLL with life because we don't know what we are missing in the absence of Beis Chayeinu.
