In a fit of depression, one is much less driven to engage in productive work.
Or let's reframe this: perhaps one is depressed partially because one is driven to work intellectually, and at the same time lacks the will to work, or one is deprived of the ability to work, which contributes to a diminished self concept and a general state of dissatisfaction with one's output and the world itself.
This state has structural origins. One is in a position in which one's self and one's environment are working together to sustain the depression: the opportunities to climb out are not there, or are not apparent, and besides, there is no energy available for climbing out. The state reinforces itself until it exhausts itself.
With this in mind, consider the analogous structure of an economic depression. Why do depressions happen? Why aren't they simply stimulated away and into another boom-state? We know that theoretically this is more than possible, though not without its own complications, especially further down the road.
But knowing and willing are different things, and in this case will is tied up with a conservative structure which accounts for the persistent accumulation of capital itself, which is in turn partially regulated by a moral logic of its own.
This moral logic contains strains of what is often called the Protestant work ethic, an overhanging religious sensibility that posits hard work as an unqualified good. This divergent outgrowth of religious sensibility was probably in part a reaction to the attempted Catholic monopoly on all spiritual activity. One is moral if one is constantly working to better one's self and society, a type of working that incidentally has its basis in specific social, political, and material conceptions of "better."
So capitalists, having outsized access to the levers of power, have nothing but contempt for the notion that a depression should be stimulated away with social spending and public works, that the common workers had to "pay" in sweat and blood for the depression, and work themselves out of their holes or die trying, and the capitalists were just the class to provide this opportunity.
This pseudo-morality was used in rationalizations for removing peasants off of the land throughout the birth of capitalism, and in later imperialist ventures as well. The peasants and "savages" were lazy and indolent, making them morally corrupt, and it was a moral act to forcibly remove them and work the land as it should be worked. This notion was ever-present in conceptions of progress.
The growing mercantilist nation-state was the vehicle for this productive accumulation and growth, and then slowly the private actor pulled away in power. Like fire leaping ravenously across grains of sawdust, disintegration paradoxically produced explosive capitalist growth.
Consider one of the characteristic symptoms of an overblown work ethic: the irresistible urge to be doing something, preferably something constructive which is geared toward some end. What is constructive? What is to be the end? A political decision.
But what happens when one is simply doing nothing? In a milieu of theoretical plenty, is this so catastrophic? One sleeps, giving the relaxed brain an opportunity for house cleaning. One fasts, and a relaxed metabolism reverts to toxin removal. And etc.
So modern work is not in fact bound up with necessity or the persistence of our species, but an overflowing and an overabundance which necessarily overshoots its mark, and crashes, constantly antagonizing its surroundings and reproducing turbulence.
Capital concentrates, and sheds, and destroys whatever it couples with, necessitating a restructuring that reabsorbs the antagonistic detritus and the cycle begins again. The moral logic compels one to work on; it must not stop. GDP-coupled emissions must be generated. E waste must be shipped to Africa. Torrents of food must be produced and then tossed away. Plastic, phosphorous, and nitrates must flow out into the ocean. A gasp of toxins and the system panics; we must work harder!
