What do northerners tell us when they eat ling?

The story tells us that knowledge is endless and people can't know everything.

Northerners Eat Ling is a classical Chinese written by Jiang Yingke in Ming Dynasty, which is from Xue Tao's novel. The story of "Northerners Eat Water Chestnuts" is about a northerner traveling to the south. After he saw the water chestnut, he ate the shell together because he didn't know its characteristics. As a result, he made a joke This story tells us that people can't know everything, so they should pretend to know.