During the Song Dynasty, there was a scholar named Tao Gu, also known by his courtesy name Xiushi, who had a great fondness for crabs.

On one occasion, Tao Gu was sent by the imperial court as an envoy to the Kingdom of Wuyue, one of the Ten Kingdoms during the Five Dynasties period (covering parts of present-day Zhejiang, southwestern Jiangsu, and northeastern Fujian). King Zhongyi of Wuyue, aware of Tao Gu's preference, prepared a lavish banquet featuring over a dozen varieties of crabs, arranged from largest to smallest.

Upon seeing them, Tao Gu chuckled and said, "This is truly 'one crab not as good as the next'!" Originally, "一蟹不如一蟹" (yī xiè bù rú yī xiè) literally meant that each crab was inferior to the one before it. Later, this phrase evolved into an idiom, widely used to describe a declining trend where each successive item or situation is worse than the one that came before it.