Status Updates From Wealth of Nations

1.3
Labour can only really be split up, if there is a certain density of jobs. People living in the vast countryside cannot specialize in one specific thing, as they will not be able to trade.
Rivers and navigable seas massively support the cheap supply of trade, making it easier for people to specialize.

1.2
Men only act for their own wellbeing. Everyone, like in nature, has to care for themselves, so one only takes up a job, if they can be assured, that trading their product or service brings themselves more what they need for life, than actually getting these things themselves.

1.1: A society is more productive when Labour is split. Everybody should only be employed in 1 very specific task. That way they get better, faster and cheaper. That differs prosperous nations from not so prosperous ones.
That’s not really possible (due to seasons) in agriculture. Therefore their products remain of the same price for equal quality.