Many people see the simple truth but don't feel it deeply or even agree with it. Without corresponding experience, they can't realize this until they reach the realm. It is like a magical secret book. It takes time to experience it, realize it in practice, gradually deepen its skill, and truly realize its mystery when it reaches the realm.
In the information age, a lot of knowledge can be easily obtained, but many truths that need a lifetime can be read in books, so this is the best era in the long river of human history. Knowledge is cheap and easy to be ignored.
In ancient times, knowledge was monopolized by nobles, and books were precious. Learning from a teacher requires three visits and nine knocks, and tea and water are served. Only when you are comfortable can you teach a trick and a half, and the master will hide one hand. Modern teachers generally don't keep secrets and teach students generously, but many students don't want to learn, and they don't pay attention to it.
Knowledge is the result of predecessors' efforts, and even the precious experience accumulated in one's life is the crystallization of wisdom summed up in constant practice. Knowledge is priceless and hard to come by. We should respect and cherish it.