Exactly 50 years ago this time of year, a 51-year-old man handwrote a four-page letter on a legal pad to his then 21-year-old son, one of seven children – six of them sons and one angel of a daughter – who was spending a semester studying in Dublin, Ireland. The letter’s narrative arc, now mostly a lost art, began by directly addressing the gift of the moment to both the writer and the...