Meng's book is sincere, and the stone is open, which means that people's sincerity can touch the world and make the stone crack. This is a metaphor, as long as they concentrate on doing it sincerely, any difficult problem can be solved. It describes a sense of sincerity towards people.
From: "Zhuangzi Fisherman": "The true person is sincere, not refined and sincere, and cannot be moved." Wang Hanchong's On Balance and Feeling Deficiency: "Sincerity opens the stone."