At either the end of chapter 10 or chapter 11 of Capital vol. 1, Marx has a really awesome explanation of this argument that capital owners "deserve" all the profit on their investment.
Edit: it's the end of chapter 11, this section in particular but also the paragraphs before it:
the head of the firm of Carlile & Co. actually imagines that if he sells his factory, not only will the value of the spindles be paid to him, but, in addition, their power of annexing surplus-value, not only the labour which is embodied in them, and is necessary to the production of spindles of this kind, but also the surplus labour which they help to pump out daily from the brave Scots of Paisley, and for that very reason he thinks that with the shortening of the working day by 2 hours, the selling-price of 12 spinning machines dwindles to that of 10!
This is more about the capitalist who buys and sells existing businesses rather than the entrepreneur who starts a business (the former is more common than the later, btw), but the same principle applies. A capitalist starts a business and when it comes time to cash out, they assume they are owed all the surplus labor the new buyer will appropriate. And the new buyer, since they "paid" for that surplus labor, sees it as something that is "owed" to them.
At either the end of chapter 10 or chapter 11 of Capital vol. 1, Marx has a really awesome explanation of this argument that capital owners "deserve" all the profit on their investment.
Edit: it's the end of chapter 11, this section in particular but also the paragraphs before it:
This is more about the capitalist who buys and sells existing businesses rather than the entrepreneur who starts a business (the former is more common than the later, btw), but the same principle applies. A capitalist starts a business and when it comes time to cash out, they assume they are owed all the surplus labor the new buyer will appropriate. And the new buyer, since they "paid" for that surplus labor, sees it as something that is "owed" to them.