抛砖引玉　(pāo zhuān yǐn yù)

Throw out a Brick to Attract a Piece of Jade

This phrase is now widely used as an idiom. It usually means that one makes some trite remarks first in order to tease others into spelling out their more valuable and insightful opinions or ideas. Many speakers tend to use it to show their modesty.

One story behind this saying is about a fan of Zhao Gu, a famous poet in the Tang Dynasty (618-907 AD). The fan wrote down a few lines of verse on the wall in an attempt to draw the attention of the poet and spur him into completing the poem. His trick actually worked.

However, when this phrase is used as a scheme, it means to sacrifice something cheap as a bait to lure your enemy into reacting to it and then you try to get something much more valuable from him in return.

Here is one of many stories often used to illustrate this scheme.

During the Spring and Autumn Period (770-476 BC), the king of Chu sent out an army to attack a small state named Jiao. The two sides stood off around the capital of Jiao and the Chu troops found it quite difficult to take the city as it was fortified by high and solid defense walls.(https://www.daowen.com)

One of the aides talked to the king of Chu, suggesting to send out small squads of unarmed soldiers disguised as local farmers collecting firewood to lure the enemy to come out and attack them.

“Jiao is a small country, but the ruler and his people are light-headed and imprudent. So, they are susceptible to illusions,” said the aide.

The next day, the king of Chu sent out 30 soldiers to collect firewood on a nearby mountain. They all wore tattered farmer’s clothes and carried no arms.

When the ruler of the besieged state saw them from the city wall, he ordered his troops to chase and capture them. As a result, all the 30 Chu soldiers were seized and brought back into the capital town.

The day after, the Chu king sent out more soldiers in farmer’s clothes to collect firewood. The ruler also sent out more troops to capture them on the mountain.

This time, the Jiao troops were ambushed in the valley and lost most of their men. At the same time, the Chu soldiers took some captives as hostages to force the Jiao ruler to surrender and sign an unequal treaty.

The Chu king used a few soldiers as a “brick” and tossed them out as a bait. In return, he harvested the “jade” of winning the battle and forcing the unwary and overconfident ruler of the small kingdom to surrender.