Marx considered the capitalist class to be the most revolutionary in history, because it constantly revolutionized the means of production. But Marx argued that capitalism was prone to periodic crises. He suggested that over time, capitalists would invest more and more in new technologies, and less and less in labor. Since Marx believed that surplus value appropriated from labor is the source of profits, he concluded that the rate of profit would fall even as the economy grew. When the rate of profit falls below a certain point, the result would be a recession or depression in which certain sectors of the economy would collapse. Marx understood that during such a crisis the price of labor would also fall, and eventually make possible the investment in new technologies and the growth of new sectors of the economy. Marx believed that this cycle of growth, collapse, and growth would be punctuated by increasingly severe crises. Moreover, he believed that the long-term consequence of this process was necessarily the enrichment and empowerment of the capitalist class and the impoverishment of the proletariat.