An old woman in Candide (by Voltaire), is relating her own life and her sufferings:

I have been a hundred times upon the point of killing myself, but still I was fond of life. This ridiculous weakness is, perhaps, one of the dangerous principles implanted in our nature. For what can be more absurd than to persist in carrying a burden of which we wish to be eased? To detest, and yet to strive to preserve our existence? In a word, to caress the serpent that devours us, and hug him close to our bosoms till he has gnawed into our hearts?

but more importantly is how the old woman ends up her speech:

prevail upon each passenger to tell his story, and if there is one of them all that has not cursed his existence many times, and said to himself over and over again that he was the most wretched of mortals, I give you leave to throw me headfirst into the sea

For that reason it is interesting that in the movie My life as a dog, a kid keeps comparing his troubles with the sufferings that Layka must have endured while traveling to space and dying in the process.

And then there is The Gadfly (by Ethel Lillian Voynich), which asks what is the meaning of the suffering of Jesus? And what if you believe in Jesus and are asked to select between him and your own son, who has had a more painful life and death?

But anyways, I digress, the main point of Candide is to question (or ridicule?) the rationalist optimism of "all is well in the world", similar to Aldous Huxley's Brave New World:

"Fortunate boys!" said the Controller. "No pains have been spared to make your lives emotionally easy-to preserve you, so far that is possible, from having emotions at all."
"Ford's in his flivver," murmured the D.H.C. "All's well with the world."