Marx concentrated on the"surplus value "-what we call profit. Workers produce things but get paid only a fraction of the value of what they produce. The capitalist owners skim off the rest, the surplus value. The working class-what Marx called the proletariat - is paid too little to buy all the products the workers have made, resulting in repeated overproduction, which leads to depressions Eventually, argued Marx, there will be a depression so big the capitalist system will collapse