The second engine of growth is the accumulation of capital, driven by saving and the opportunity for profit. Smith said that growth can be reduced by commercial failures, a lack of resources required to maintain the fixed capital stock, an inadequate money system (there is more growth with paper money than with gold), and a high proportion of unproductive workers. He claimed that capital is more productive in agriculture than in manufacturing, which is higher than in trade or transport. Ultimately, the economy will grow until it reaches a wealthy, stationary state. In this, Smith underestimated the role of technology and innovation - the Schumpeterian growth described earlier.