Long ago, a man named Ai Zi from the Central Plains had never seen the ocean.
One day, the scholar Aizi arrived at the seashore, where the vast blue ocean stretched endlessly before him, its waters salty to the taste. Filled with sudden excitement, he begged a fisherman to take him out to sea.
A fisherman pulled in his net and found, besides fish, a strange creature with a dark shell—round top and bottom, flat sides, five pairs of legs, the first pair like pincers that could snap sideways, and it crawled sideways, some as heavy as a whole catty.
Pointing at the creature, Ai Zi asked eagerly, "What is that?" The fisherman laughed heartily and replied, "You've never even seen a swimming crab? What a fool!" "Can it be eaten?" Ai Zi pressed. "Of course," the fisherman said with relish, "and it tastes quite good—especially the male's roe and the female's golden cream, absolutely delicious!" Ai Zi nodded repeatedly, committing it all to memory.
Soon after, Ai Zi encountered another strange creature resembling a swimming crab, only slightly smaller, with the largest weighing no more than half a jin.
"Are these what you call swimming crabs?" Aizi asked. The locals good-naturedly teased him before explaining, "Swimming crabs live in the salty waters of the sea. These are also crabs, but they live in freshwater—everyone calls them river crabs." Aizi nodded, "Oh, oh." Later, he discovered a creature that looked like a crab but was much smaller, its shell no bigger than a coin. Chuckling, he asked, "Is this still called a crab?" The locals replied, "It's a type of crab called a marsh crab."
Ai Zi looked up to the heavens and sighed, "Heavens above! You have created things so alike yet so different!" He glanced around, as if questioning or mocking, "Why is each crab worse than the last?"
The entire room burst into laughter.
Later, the idiom "One crab is worse than the last" came to describe each one being worse than the previous.
Source: *Aizi's Miscellany* by Su Shi
Meaning of the Idiom: Later, the Chinese idiom "一蟹不如一蟹" came to describe each one being worse than the previous.