4 ideas
Because people pursue profit as naturally as water flows downhill, the best ruler goes along with that pursuit. The next best guides it with incentives, the next teaches, and the next regulates by force. The worst competes with the people for profit, as state monopolies over salt and iron do.
Following the method attributed to Ji Ran, Sima Qian holds that goods at an extreme of dearness will turn cheap and goods at an extreme of cheapness will turn dear. The trader should therefore sell dear goods as if they were dirt and buy cheap goods as if they were pearls. In drought, lay in boats; in flood, lay in carts.
Sima Qian observes that the greedy merchant ends up with a return of about three-tenths, while the modest merchant who takes smaller margins ends up with five-tenths. Faster turnover compounds the smaller per-unit gain into the larger total fortune.
When Qin conquered Zhao, it deported the Zhuo family, ironworkers, to Shu. Other deportees bribed officials to be settled close by, but the Zhuos asked to be sent far away to Linqiong. They had learned that its soil grew taro, so no one there starved, and that it had iron ore. By smelting iron and trading with the local people, they came to command about a thousand servants and lived with the pleasures of a titled lord.