I was too embarrassed to ask why not, so I brooded on this for a while, and finally decided that I wasn't cut out for that discipline. When I began reading the mathematical reconstructions of the Political Economy of Smith, Ricardo, and Marx, I was pleased to see that each of the equations had a little Greek letter pi, which stood for the profit rate.
Eventually, I came to understand that the centerpiece of Marx's economic theory is his claim that capitalism rests on the exploitation of the working class, from whom profit is extracted by capitalists in the form of surplus labor value. Despite my theoretical criticisms of the concept of surplus value, I clung tightly to the notion of exploitation as the source of profit, inasmuch as it seemed to me to be the deepest and most fundamentally true idea I had encountered in my long autodidactic study.
How could the manifestly brilliant men [mostly] in the discipline of academic economics have missed a truth that struck me as virtually self-evident? I reminded myself of Upton Sinclair's oft-quoted observation: "It is difficult to get a man to understand something, when his salary depends upon his not understanding it!"