Yes, We CAN!
When the spies came back and declared "we can't" inherit the land of Israel, the entire nation wept that night in their tents. And Hashem declared that "since you cried on this night for nothing, you will cry on this night for generations". The crying for generations that we cry, is the mourning over what we always said "we can't" do.
This notion of "we can't", is the source of all mourning. It is the source of all physical and spiritual failures. Hashem is behind us. There is NOTHING we can't do. But we are intimidated and afraid to try hard enough. We don't believe in ourselves and in Hashem enough. And that is what causes us to fail again and again. That is the root cause of all destruction.
So on this Tisha Be'Av, while we mourn the times we thought "we can't", let us focus our mourning into a powerful resolution for the future: "YES, WE CAN". Yes, it seems that the addiction is so much stronger than us, just as the fortified cities and giants appeared to be much stronger than the Jewish people's military capabilities in the desert. But if Hashem is with us, if Hashem is behind us, WE CAN DO ANYTHING.
This idea was taken from the following video clip from Aish.com