To the modern eye, the minor Jewish fast days would seem trivial and stupid, probably because they are. Not Yom Kippur when we're held accountable for our sins, nor Tisha B'Av when we commemorate the destruction of the two Temples - the double singular event that occurred on the same day and define modern Judaism, but Ta'anits like Tzom Gedaliah the day after Rosh Hashana ends to commemorate the assassination of a governor of Judah three millennia ago, or Shiva'Asar b'Tammuz, which on the one hand is the day Moses broke the two tablets. But that's not the reason we fast on Shiva-Asar b'Tammuz. The reason is that this is supposedly a day when terrible things keep happening in Judaism. It's not the day of the Temple's destruction but the daily sacrificial offering ceased to be brought because the walls of Jerusalem were breached! It's the day the Roman General Apostamus, my god, burned a Torah Scroll! It was the day an idol was erected in the Temple!
It's impossible to have any idea how significant or trivial these events seemed at the time, but with the distance of twenty-five hundred years, this all seems a bit much. If you affixed a fast day to every Jewish tragedy of that importance, when would Jews eat?
But Assarah B'Tevet's the stupidest. It's apparently not enough to have a fast day for the destruction of the Temple destroyed, we need a fast day too for when the walls of the city were breached. Fine enough. It also commemorates the two days before. Shmoneh b'Tammuz when the Bible was first translated into Greek, apparently thereby etoliating the Bible of its divine spirit emanating from the Hebrew original. That seems debatable, but one can understand why this would be a tragedy as it would strip Jews of their of sole dominion over their holy book and cause Christian dominion over them. But the kicker is Tisha b'Tammuz, of which the text of the Shulchan Aruch literally says "Something happened, but we do not know what it was."
The Jewish calendar frankly needs some updating. To have fast days for the assassination of Gedaliah and Apostatamus burning a Torah Scroll is seriously unprioritized when there's no fast for the Shoah or the Alhambra Decree.
But fast days result in a fate against which all Jewish mothers strenuously warn and fight against like a dybbuk at the door. Eat, you'll have low blood sugar." "You're just mad because you have low blood sugar." "I told you not to play sports or do your homework or give that presentation when your blood sugar is low!" The symptoms of the dreaded low blood sugar include cold sweating, dizziness and headache, rapid heartbeat, slurred speech, and muscle twitches. But while every Jewish mother secretly believes her child is perpetually about to die, none admit it. What they're really looking for is personality changes, confusion and irritability, anxiety and inability to concentrate, and to keep their children from these future-damaging symptoms, they're willing to tolerate an extra thirty or forty pounds on their growing boys, which causes them to dread that they've traded their children's long-term health for prospects at overachievement.