We all like usefulness and don’t like uselessness. But what usefulness and uselessness is usually depends on people, setting and timing.

What does “unintentional usefulness is called the greatest usefulness” mean?
In Taoism we usually talk about “Natural Way of Tao’ and “Wu-Wei”(Without Deeds, Doing Nothing). Historically, I think many great inventions, discoveries and creations were unintentional. Before they made them, these people didn’t think their job would change or affect our lives. Like Newton’s discovery of the Laws of Gravity and Einstein’s presentation of the Theory of Relativity, I believe that these men didn’t ponder whether their work would be useful to humans or not. They just wanted to find an answer for their questions. But we all know their theories are very important to us.

Here is a Taoist story:
One day Zhuang-Zi wanted to visit Zhuang-Zi’s friend with his student. While walking on a mountain path, Zhuang-Zi noticed a few huge trees with lush leaves, which the lumbermen didn’t cut. He asked one of the lumbermen: “Why didn’t you fell these trees?” The lumberman answered; ”These trees could grow so tall precisely because they are useless.”
When Zhuang-Zi descended the mountain, he dropped in on a friend of his. His friend very glad to see him and ordered a servant to slaughter a chicken for their meal. The servant asked his master; “Between the two chicken we have, one cackles and the other doesn’t. Which one shall I slaughter?” The master said: “ Slaughter the one that doesn’t.”
After the meal Zhuang-Zi’s student asked Zhuang-Zi, “I have one thing I just don’t understand…yesterday, the trees in the mountain were spared because they were of no use to anyone. Today, this chicken gets slaughtered because it is also useless. How shall we position ourselves in this world?” Zhuang-Zi replied: “ It looks like I will be caught between usefulness and uselessness and that is going to create a burden on me. So it is best to adapt to changes as they come and disregard usefulness or uselessness; just follow the natural way of Tao, and you will be a freeman.”
“All worldly moral standards are relative standards. Hence usefulness and uselessness are relative concepts. A man of great wisdom would do well to look beyond relative moral standards.” Zhuang-Zi said.

When we look at the sky and earth they look like they remain peacefully unmoving, yet the seasons change and are seldom known to rest. The sun and the moon hasten through their courses day and night, yet their befitting light has not changed through the ages.
Mother Nature uses the sound of no sounds to show us how “unintentional usefulness is the greatest usefulness”.