Here, tea ceremony and humanity are used to reveal philosophy: through tea ceremony, natural truth can also be realized, and humanity is the way of the soul. Character can be observed through tea ceremony, which is also a part of people's mind. It is easy to say and understand. For example, Lu Yu's Tea Classic clearly explains the tea ceremony. Human nature is hard to say, that is to say, human nature is the most complicated and difficult to fully explain. Either you can't say it, you can't say it directly, or you are talking nonsense.
In short, people and society are the most difficult to tell clearly.