A statement from Bobonne, Luckas Vander Taelens' grandmother and his childhoods guide through the labyrinth of human despair. She had an answer to most questions about the sense and nonsense of life.
This one "A chaque jour suffit sa peine" means something like "Each day has enough of its trouble".
The idea that one grief per day is enough for a mortal, was her way to mollify a cruel God not to send more mischief her way.
It also suggests a person should not be bothered with too many issues at once.