Excessive application, during four days of the week, is frequently the real cause of the idleness of the other three, so much and so loudly complained of. Great labour, either of mind or body, continued for several days together is, in most men, naturally followed by a great desire of relaxation, which, if not restrained by force, or by some strong necessity, is almost irresistible. It is the call of nature, which requires to be relieved by some indulgence, sometimes of ease only, but sometimes too of dissipation and diversion. If it is not complied with, the consequences are often dangerous and sometimes fatal, and such as almost always, sooner or later, bring on the peculiar infirmity of the trade. It will be found, I believe, in every sort of trade, that the man who works so moderately, as to be able to work constantly, not only preserves his health the longest, but, in the course of the year, executes the greatest quantity of work.
Adam Smith, The Wealth of Nations