For contemplation on those dark, likely wintery, days:

Slumping down as another dim, cloudy, grey winter day barely wakens workers at their computers or during their commutes, perhaps a nod of understanding to the greenery of vegetation could help one to appreciate our energetic advantages on such days.

For while we may, actually, harvest sunlight in reactionary processes, for example stimulating the conversion of a single photon of light energy against the retina of the eye to a protein that helps us see in shade or during night, and also in other reactions to trigger processes regarding our daily (circadian) rhythms, and for these reasons find that days of light limitation can prevent our brains from fully coming into cognizance, but could you imagine if your metabolic energy processing also depended on the receipt of those same, scattered photons of sunshine filtered through thick vapor of clouds, or barely passing over the horizon?

You would not even be able to consume the food you may feel a bit sick and too tired to lethargically poke at during meals on such days, because there would be just a few crumbs on your plate that you would be caught snoring next to.

You may then, in such a situation, also choose dormancy, not waking like the hibernating bear for a midnight snack, or persistently moving about for bits of food like the bullfinches and chickadees, instead really hunkering down more like a computer in sleep mode or evergreen plants, such as conifer trees, in winter. You could alternatively, if your meal was from the sun, close all nonfunctioning programs or delete them, as do deciduous plants in dropping away any unnecessary tissue they cannot currently utilize, let alone maintain, in times of such light scarcity.

Retaining only the core and most basic of metabolic processing, plants cannot forever withstand the dark, so that their photosynthetic strength of feeding from the sun can also be a weakness, when the world turns to face away from that large star, warm yet so very far away. Plants can persist through episodes of dark, but you might consider the advantages you have to gaining energy elsewhere than the sun, even if you should find yourself terribly sleepy, not the sharpest, and also waiting for its seasonal return.