The Wealth of Nations by Part 1 Chapter 9 Page 25

occasional losses to which every employment of stock is exposed. It is this surplus only which is neat or clear profit. What is called gross profit comprehends frequently, not only this surplus, but what is retained for compensating such extraordinary losses. The interest which the borrower can afford to pay is in proportion to the clear profit only.

The lowest ordinary rate of interest must, in the same manner, be something more than sufficient to compensate the occasional losses to which lending, even with tolerable prudence, is exposed. Were it not more, charity or friendship could be the only motive for lending.

In a country which had acquired its full complement of riches, where in every particular branch of business there was the greatest quantity of stock that could be employed in