The city is like a huge sponge, and the labor force is like water flowing between urban and rural areas. When the economy is in the upward period, economic expansion will absorb more labor force; when the economy is in the downward period, the economic recession will push these labor forces back to the countryside. It is the sponge effect caused by China's urban-rural dual structure, It has played a role as an employment buffer in the financial crisis. However, this sponge effect is unsustainable, because one of China's basic national conditions is that the agricultural surplus labor force should be transferred to cities.
intended to illustrate that:
We should not rely too much on the employment buffer effect of sponge effect