In her book Family Ministry, Diana Garland relates the following account by R.L. Honeycutt on the origin of the Irish expression "Chancing one's arm":

On display in St. Patrick's cathedral in Dublin hangs an ancient door with a rough hewn, rectangular opening hacked in the center. The story of this "door of reconciliation" and the related Irish expression of "chancing one's arm" are remarkable and instructive.

In 1492, two prominent Irish families, the Ormonds and Kildares, were in the midst of a bitter feud. Beseiged by Gerald Firzgerald, Earl of Kildare, Sir James Butler, Earl of Ormond, and his followers took refuge in the chapter house of St. Patrick's cathedral, bolting themselves in.

As the seige wore on, the Earl of Kildare concluded the feuding was foolish. Here were two families worshiping the same God, in the same church, living in the same country, trying to kill each other. So he called out to Sir James and, as an inscription in St. Patrick's says today, "undertoake on his honour that he should receive no villanie."

Afraid of "some further treachery," Ormond did not respond. So Kildare seized his spear, cut a hole in the door, and thrust his hand through. It was grasped by another hand inside the church. The door was opened and the two men embraced, thus ending the family feud. From Kildare's noble gesture came the expression "chancing one's arm."