-Mencius

Scholars must first doubt.

-Cheng Yi (philosopher and educator of the Northern Song Dynasty)

People who are suspicious of ghosts have never learned; Learning requires doubt.

-Zhang Zai (philosopher of the Northern Song Dynasty)

Those who learn without doubt will teach those who have doubts, and those who have doubts will have no doubt, and there will be progress in this respect.

-Zhu

The predecessors said that learning is expensive and there are doubts, small doubts and small progress, big doubts and great progress. Skeptics have a chance to realize. Awakening and progress.

-Chen Xianzhang (Ming Dynasty thinker and calligrapher)