The designer who took the card away, and found the defense still standing.
John Burton is an independent game designer who set himself a puzzle Prim finds rather wonderful. Keep the American rules and the American tiles, take the card of hands away altogether, and see what is left of the game. What he built is Card Free American Mah Jongg, which runs on a short set of rules about how numbers and suits may be grouped, in place of a printed list. He loved the play of the American game, borrowed ideas from the Hong Kong, Sichuan and Japanese styles to build on top of it, and playtested it with real players.
Experienced American players asked him a fair and worried question: without a card, how could anyone play defense? His answer, in a post cheerfully titled "Defense? Yes you can!", is why Prim featured him. You play defense the way you always did, by reading the exposures and the discards. Take the card away and the defense survives, because it never lived on the card. It lives out in the open, in what the table has already shown.
Written from what the letter said. Read the letter for the whole of it.