Sometimes it is easier to see the light when you stand partly in the darkness.
In the quote from Garth Nix's Mister Monday, it suggests that gaining perspective can often come from experiencing contrasting situations. Standing in the darkness allows one to better recognize and appreciate the light, implying that difficulties or challenges can illuminate what is good or positive.
This idea emphasizes the importance of contrast in understanding and appreciating different aspects of life. Sometimes, facing hardships helps individuals to see the value of happier moments and to find clarity by experiencing both sides of a situation.