Ask why this pond stays so clear: because living water keeps flowing from its source.
問渠那得清如許、為有源頭活水来。

Philosophers
Zhu Xi
Southern Song Confucian (1130-1200), the systematizer of Neo-Confucianism. His Four Books commentaries served as China's civil-service exam basis from 1313 to 1905, shaping East Asia's governing class for six centuries.
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Source: 朱熹『観書有感二首』其一 (詩集所収)Verified