One of Vonnegut’s rules of writing:
Be a sadist. No matter how sweet and innocent your leading characters, make awful things happen to them—in order that the reader may see what they are made of.
And it’s true. You don’t understand characters by seeing what they do when the world is happy and fluffy all around them, you understand those characters by seeing what they do when brain-eating zombies are marching towards their grandmother; do they run away and live, or do they run to help and risk death? Or what do they do after watching those zombies eat their grandmother because they did nothing?
Of course there are limits; it takes the right kind of sadism to fit the story. If your characters are repeatedly being raped by monkeys then the readers may be spending more time trying to figure out quite how perverse the author’s mind is than concentrating on the characterisation.