simcha is not despite the tragedies; it is BECAUSE of the tragedies : short vort

The best way to say this is by a vort. In shir hama’alos we say ‘when we will return to Zion we WERE dreaming.’ Why is dreaming in the past tense when the rest is in the future? Answers Rav Nevetzhal that when the redemption comes, we will look back at tragedies in history and realise that they WERE all for the good and were necessary steps in bringing the redemption. The idea is that tragedies cause redemption. In the Tisha B’Av kinnos (number 45; eli tziyon) we tell the city of Zion to wail ‘like a woman suffering from birth travail,’ for we are expressing the above idea that just like the pains of labour produce the joy of a child, so too do the pains of exile ultimately produce future redemption. And it is interesting to note that Pesach and Tisha B’Av always fall on the same day of the week – this means that the depths and pains of tragedy of Tisha B’Av are linked to the joyous redemption of Pesach; for the pains and tragedies ultimately bring about the redemption. And this is so much of what we do on seder night; we start the story way back when Avraham was born to idol worshippers and go throuh to yetzias mitzrayim to show this idea; that we saw that the lows of history caused the eventual redeption.