After Emperor Taizong Li Shimin seized the throne through the "Xuanwu Gate Incident" in 626 AD, he learned from the rapid fall of the Sui Dynasty by strengthening official assessments, expanding the imperial examination system, and selecting talented individuals. These measures contributed to political stability and social prosperity in the early Tang Dynasty.
That year, after the imperial examinations, the list of new jinshi (successful candidates) was announced. Emperor Taizong of Tang, accompanied by only a few attendants, quietly went to the Duann Gate to observe the newly selected scholars. The candidates, with solemn and respectful expressions, filed out of the gate in an orderly manner one after another. Seeing this scene, the emperor was overjoyed and, clapping his hands with laughter, exclaimed, "All the heroes under heaven have fallen into my snare!"
"Gou" refers to a crossbow. "Gouzhong" means within the arrow's range, metaphorically a trap or control. The idiom "All Enter the Gouzhong" means completely under control or entirely caught in a snare.
Source: Wang Dingbao (Five Dynasties), *Tang Zhi Yan*, Chapter "On Presented Scholars"
Meaning of the Idiom: Later, the Chinese idiom "尽入彀中" came to describe All Enter the Gouzhong means completely under control or entirely caught in a snare.