St. Patrick led a pretty interesting life. He was kidnapped from him home in Scotland at 16 or so (he came from a well to do family) and was a slave in Ireland for 6 years while it was still pagan. While there he began to have visions. He would eventually escape back to Scotland in part due to these visions, and then returned to Ireland of his own free will to facilitate the spread of Christianity there, a job which often put his life in jeopardy yet again. The shamrock thing likely came as an analogy he used to explain the holy trinity.

How that led to us pinching other for not wearing green is the real mystery here..

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We are what we repeatedly do - Aristotle