https://en.wikipedia.org/wiki/Fiat_justitia_ruat_caelum
>The falling sky clause occurs in a passage of Heauton Timorumenos, by Terence, suggesting that it was a common saying in his time. In the scene, Syrus suggests a scheme through which Clinia might deceive another into taking actions that would further his love interests. Syrus lays out his plan, while Clinia, who must act it out, finds faults with it, finally asking, "Is that sufficient? If his father should come to know of it, pray, what then?" To which the Syrus replies, "Quid si redeo ad illos qui aiunt, 'Quid si nunc cœlum ruat?'"—"What if I have recourse to those who say, 'What now if the sky were to fall?'", the suggestion being that Clinia has no other options available, so to worry that the plan will, obviously, fail if the father finds out makes no more sense than worrying about the fact that it will also fail if the world were to suddenly end.