I remember that George Eliot talked somewhere or other (in her letters? in an essay? perhaps in one of the novels) about tiredness, listlessness; about how, in order to do anything, you have to build and maintain a mental bridge of energy over the abyss of physical and intellectual tiredness.
I don’t know about a bridge of energy – it sounds exhausting before you even start – but that sense of conscious focus in performance unites Bruegel’s beggars and Degas’s dancers. It is something we all do, perhaps especially as we age – drag ourselves up by our bootstraps, up to the vertical, on a more or less daily basis. We drape our necessary roles over a concealed (or ill-concealed) core of ennui, of exhaustion.