It’s Arya who remembers it.
Back at Winterfell, they had eaten in the Great Hall almost half the time. Her father used to say that a lord needed to eat with his men, if he hoped to keep them. “Know the men who follow you,” she heard him tell Robb once, “and let them know you. Don’t ask your men to die for a stranger.” At Winterfell, he always had an extra seat set at his own table, and every day a different man would be asked to join him. One night it would be Vayon Poole, and the talk would be coppers and bread stores and servants. The next time it would be Mikken, and her father would listen to him go on about armor and swords and how hot a forge should be and the best way to temper steel. Another day it might be Hullen with his endless horse talk, or Septon Chayle from the library, or Jory, or Ser Rodrik, or even Old Nan with her stories.
Arya had loved nothing better than to sit at her father’s table and listen to them talk. (Arya II, AGOT)
As you can see from the quote, Ned talked to them about their jobs and learned a bit about their work, as part of his philosophy of enlightened paternalism.
This is something of a classic move of noble/commoner interaction; before the term “condescension” became a pejorative, the ability of a nobleman (especially a king) to be polite to the lower orders without erasing the social distance between them (such “overfamiliar” behavior, it was believed, would give rise to either contempt and the loss of aristocratic mystery or overfamiliarity and social climbing) was seen as a necessity for elite behavior. Hence, it’s something of a cliche in the U.K to write about royals pressing the flesh with their subjects and saying things like “Hello, what’s your name? And what do you do? That’s so interesting! And how long have you been a(n) ______? Jolly good!”
Ned’s better at it than that caricature, but there’s still a political motive behind his custom: from later in the chapter, “Her father used to say that a lord needed to eat with his men, if he hoped to keep them. “Know the men who follow you…and let them know you. Don’t ask your men to die for a stranger.” As I’ve said elsewhere, Ned’s person-focused theory of politics is a disadvantage when it comes to being Hand of the King, but if you look at the long run, it inspired loyalty from beyond the grave.
In terms of where he learned it, I don’t think he learned it from Jon Arryn – the Vale is far too socially conservative for that to be Jon’s M.O. Rather, I think it’s something that Ned learned from his father, that it’s part of the Starks’ unique relationship with the people of the North. I think Cat was initially scandalized, but eventually accepted as part of the Northern way.
