The recent troubles in Tibet are a replay of events that happened two decades ago. On Oct. 1, 1987, Buddhist monks were demonstrating peacefully at the Barkor — the famous market street around the central cathedral in Lhasa — when police began beating and arresting them. To ordinary Tibetans, who view monks as “treasures,” the sight was intolerable — not only in itself, but because it stimulated unpleasant memories that Tibetan Buddhists had been harboring for years.