List's theory of "national economics" differed from the doctrines of "individual economics" and "cosmopolitan economics" by Adam Smith and J.B. Say. List contrasted the economic behaviour of an individual with that of a nation. An individual promotes only his own personal interests but a state fosters the welfare of all its citizens. An individual may prosper from activities which harm the interests of a nation. "Slavery may be a public calamity for a country, nevertheless some people may do very well in carrying on the slave trade and in holding slaves." Likewise, activities beneficial to society may injure the interests of certain individuals. "Canals and railroads may do great good to a nation, but all waggoners will complain of this improvement. Every new invention has some inconvenience for a number of individuals, and is nevertheless a public blessing". List argued that although some government action was essential to stimulate the economy, an overzealous government might do more harm than good. "It is bad policy to regulate everything and to promote everything by employing social powers, where things may better regulate themselves and can be better promoted by private exertions; but it is no less bad policy to let those things alone which can only be promoted by interfering social power."