While hardly universal, many shadar-kai see their primary mission on the Material Plane as strangling the joy out of the world to make it more like the despairing wastes of the Shadowfell. While most of the cursed elves need to content themselves, or whatever the shadowed equivalent of contentment is, mirth thieves directly tap the sources of joy by using their knives to carve out feelings of happiness and bliss from their victims' minds.