“[In T.Yerushalmi Yoma 1:1] Our sages explain: ‘Every generation for which the Temple isn’t rebuilt, is as though the Temple was destroyed for that generation.’ If so, a fast day isn’t really a sad day, but an opportune day. It’s a day when we’re empowered to fix the cause of that first destruction, so that our long exile will be ended and we will find ourselves living in messianic times—may that be very soon. – Chabad.org