Hope

“And why are you so firmly, so triumphantly, convinced that only the normal and the positive--in other words, only what is conducive to welfare--is for the advantage of man? Is not reason in error as regards advantage? Does not man, perhaps, love something besides well-being? Perhaps he is just as fond of suffering? Perhaps suffering is just as great a benefit to him as well-being? Man is sometimes extraordinarily, passionately, in love with suffering, and that is a fact.”
― Fyodor Dostoevsky, Notes from Underground, White Nights, The Dream of a Ridiculous Man, and Selections from The House of the Dead

“He soon felt that the fulfillment of his desires gave him only one grain of the mountain of happiness he had expected. This fulfillment showed him the eternal error men make in imagining that their happiness depends on the realization of their desires.”
― Leo Tolstoy, Anna Karenina

“The awful thing is that beauty is mysterious as well as terrible. God and the devil are fighting there and the battlefield is the heart of man.”
― Fyodor Dostoevsky, The Brothers Karamazov

“Toska - noun /ˈtō-skə/ - Russian word roughly translated as sadness, melancholia, lugubriousness.

"No single word in English renders all the shades of toska. At its deepest and most painful, it is a sensation of great spiritual anguish, often without any specific cause. At less morbid levels it is a dull ache of the soul, a longing with nothing to long for, a sick pining, a vague restlessness, mental throes, yearning. In particular cases it may be the desire for somebody of something specific, nostalgia, love-sickness. At the lowest level it grades into ennui, boredom.”
― Vladimir Nabokov