Is there a hint for that in the game somewhere? I'm not up to that yet as I keep restarting trying to optimize a hard mode run (up to the festival of greed around day 40 or so which feels very good)
The villagers' dialogue hints at it (iirc they say if there had been enough bombs Aaron wouldn't have been injured). Also you can see the last orb in the demon domain, you can't reach it but you can tell it has to be done from the quarry. There was supposed to be much more of this kind of puzzle here but it got cut, leaving only this one that almost everyone misses.