As humanity reaches toward the moon with visions of million-person cities, a new scientific study offers a quieter, older kind of wisdom: that the limits of a place are not negotiable by ambition alone. Researchers have found that the moon's finite water ice deposits — concentrated in shadowed polar craters, unreplaced by any natural cycle — could sustain a large lunar colony for only about a century before exhaustion. The finding does not close the door on lunar settlement, but it reframes the question from how grand we can build to how honestly we can reckon with what is actually there.