“There are dark shadows on the earth, but its lights are stronger in the contrast.”
Dickens uses contrast to suggest that hardship can make moments of goodness and happiness more visible without pretending that the darker parts of life are unreal.
Source details
The Pickwick Papers, near the closing chapter, Project Gutenberg #580. The narrator deliberately leaves Pickwick and his companions in a moment of happiness and contrasts life’s “dark shadows” with its stronger lights; this is literary narration, not a promise that suffering always ends well.