This sentence comes from the summary at the end of Zhuangzi's "Human World": Everyone knows the use of useful things, but no one knows the uses of useless things.
Those who have read the masterpiece "The Human World" may be familiar with what Zhuangzi said. This long article is the attitude and dialectics advocated by Zhuangzi in dealing with people and affairs, and it is also the embodiment of Zhuangzi's philosophical views.
I once read a fable: a philosopher asked a boatman: "Do you understand philosophy?" The boatman said: "I don't understand." "Then you've lost at least half your life." Then he asked: "Do you understand mathematics?" "No," the boatman replied. "Then you lose 80 percent of your life." Suddenly, a huge wave capsized the boat and both of them fell into the water. Seeing the philosopher struggling in the water, the boatman asked the philosopher: "Can you swim?" "No." "Then you will lose your whole life". This story must be familiar to everyone. So, do you think philosophy, mathematics, or swimming are more useful?
Back to the topic, what is useful and what is useless? It mainly depends on the angle from which you stand. The Taoist school to which Zhuangzi belongs advocates the preservation of life and the preservation of life. It believes that human life is given by heaven and that people should do their best to enjoy their destiny. From this perspective, a large tree seems to be useless with crooked branches, loose trunk, poisonous leaves, and unpleasant tree smell. However, other useful trees were either chopped down and used as wooden piles, beams, or coffins. In short, they all died on the way, and only this useless tree survived. Isn’t it useless but of great use? The same goes for people. In ancient times, useful people were used by others, and they had to work hard and sometimes pay with their lives. And those who are not outstanding in all aspects and are barely making ends meet will live a peaceful life.
This is still the case in contemporary society. What kind of people are most useful nowadays? Of course, they are celebrities, bosses and Internet celebrities. They gain both fame and fortune. What kind of person is useless? Farming, serving as a soldier, doing scientific research, it’s hard work and no money. But if disaster strikes and foreign enemies invade, who will be of use? It’s self-explanatory!