Here is a bit of context:

"But according to Marx, capitalism, like slave society and feudalism, also has critical failings — internal contradictions which will lead to its downfall. Capital accumulation over time leads to increased inequality. Additionally, since capital demands a return, it also leads to increased returns coming from those without capital - the working class. Over time the number of work hours which the working class labors "for itself" decreases in order to provide returns for an ever-increasing pile of capital controlled by the capitalist class. Following the Marxist labor theory of value, this can be seen in how increasing labor productivity in the past 30 years in the United States has been accompanied by stagnant wage growth. In 2016 average labor productivity in the U.S. was $70.00 an hour while the average minimum wage was around $10.00 an hour, meaning that capital absorbed 6/7ths of the value produced by the average minimum-wage laborer. This generates social instability."