5 ideas
In the Taiping war Zeng suffered a string of humiliations. In 1854 he lost at Jinggang and tried to drown himself. Years later he wrote to his brother Guoquan that his method was to 'knock out a tooth and swallow it with the blood': absorb the defeat silently, show no complaint to superiors or rivals, and keep fighting until the position turned.
Against a more mobile enemy, Zeng refused clever manoeuvres. Every halt meant digging trenches and walls, then advancing only step by step from a secured base, as at the long sieges of Anqing and Nanjing. The method trades speed and glory for resistance to disaster. A slow army that cannot be routed eventually outlasts a brilliant one that can.
Zeng repeatedly warned his brothers that success at its peak is the most dangerous state. Unshared credit, surplus wealth and a large command draw envy from peers and suspicion from the throne. So he argued for deliberately giving away credit and shrinking one's holdings before others force it. He acted on this after taking Nanjing in 1864 by rapidly disbanding much of his Xiang Army.
Zeng reduced each domain of life to the one root that sustains it. Reading is rooted in grasping meaning, and poetry in tone and cadence. Serving parents is rooted in pleasing them, and health in avoiding anger. Fix the root habit and the rest of the domain follows.
Zeng judged that families of officials usually decline within a generation or two. Their sons grow used to servants, comfort and idleness. Families that keep farming and reading last many generations. He therefore ordered his sons and nephews to rise early, do manual household work, dress plainly and avoid acting like officials' sons, whatever the family's rank.