"because man is a social animal he owes his fellow-man, in equity, the manifestation of truth without which human society could not last. Now as man could not live in society without truth, so likewise, not without joy, because, as the Philosopher says (Ethic. viii), no one could abide a day with the sad nor with the joyless. Therefore, a certain natural equity obliges a man to live agreeably with his fellow-men; unless some reason should oblige him to sadden them for their good."
"quia homo naturaliter est animal sociale, debet ex quadam honestate veritatis manifestationem aliis hominibus, sine qua societas hominum durare non posset. Sicut autem non posset vivere homo in societate sine veritate, ita nec sine delectatione, quia sicut philosophus dicit, in VIII Ethic., nullus potest per diem morari cum tristi, neque cum non delectabili. Et ideo homo tenetur ex quodam debito naturali honestatis ut homo aliis delectabiliter convivat, nisi propter aliquam causam necesse sit aliquando alios utiliter contristare."
"unless for some reason it be at some point necessary to make others sorrowful beneficially."
Thomas Aquinas, Summa theologiae II-II.114.2.ad 1. As thomascordatus has noted, Pope Francis, in his exposition of 1 Cor 13:5 (Amoris Lætitia 99), drops "unless some reason should oblige him to sadden them for their good"! contritio dervies from conterere, not contristare.